Table of contents :

Epidemiology Aetiology Pathogenesis Symptoms & signs Laboratory examinations Differential diagnosis Therapy  Prognosis Web resources

Epidemiology : 1% of all malignant tumors of adults; 25% of all lymphomas; incidence : 3 new cases every 100,000/yr. It affects twice as many males as females and has onset at age 20-30 or > 55. Whereas the incidence of NHL has been rising since World War II, the incidence of HL has been flat. 2 age-incidence peaks have long been recognized in North America and Western Europe: young adult and older adult. In developing countries and in parts of Asia, the young adult peak is much less prominent or even absent. Several epidemiologic studies suggested an association with small family size and other factors that might result in delayed exposure to common viral infections.
Aetiology : HL can be divided into 4 entities on the basis of EBV status and age at presentation, with 3 groups of EBV-associated cases and a single group of EBV^-. The aetiology of the latter cases is obscure although involvement of an infectious agent(s) is suspected^ref.

• 35% of tumor clones have HHV-4 / EBV genome in their chromosomes (40–60% in most industrialized countries, depending on their histology) genome and antigens in the Reed-Sternberg and Hodgkin's cells^ref : a causal association between infectious mononucleosis–related EBV infection and the EBV⁺ subgroup of HD is likely in young adults. Only serologically confirmed infectious mononucleosis was associated with a persistently increased risk of Hodgkin's lymphoma. 55% of tumors obtained from patients with infectious mononucleosis had evidence of EBV. There was no evidence of an increased risk of EBV-negative HD after infectious mononucleosis. In contrast, the risk of EBV⁺ HD was significantly increased (RR = 4.0). The estimated median incubation time from mononucleosis to EBV⁺ HD was 4.1 years (IC₉₅ = 1.8-8.3)^ref. Patients with EBV-associated HL also show increased levels of EBV-infected B-lymphocytes in blood compared with normal individuals and non-EBV-associated HL cases^ref. With effective combined treatment modalities in pediatric HL, latent EBV infection has no influence on FFS but is associated with an inferior overall survival in crucial subgroups^ref. Delayed exposure to EBV is a risk factor for the development of EBV-associated HL in young adults^ref. EBV may play a role in the pathogenesis of HD by the activation of anti-apoptotic factors in a premalignant germinal center B-lymphocyte. Regardless of their role in etiology or pathogenesis, EBV-latent antigens may represent a target for possible immune therapy. Areas within the HLA class I and class III regions are associated with susceptibility to HD, the association with class I being specific for EBV⁺ disease. This finding strongly suggests that antigenic presentation of EBV-derived peptides is involved in the pathogenesis of EBV⁺ HD^ref. Serologic studies have suggested modestly higher titers to EBV antigens in patients with HD than in controls, but the differences in titers have been modest. EBV is a ubiquitous virus and the vast majority of HD patients (and adults) are EBV seropositive. EBV nucleic acids and proteins have been identified in the tumor cells in a subset of patients. Approximately 30% of HL in the USA and North America harbor these nucleic acids and proteins, while much higher percentages of tumor cells show evidence of virus in some developing countries (approaching 100% in parts of Latin America, Africa and Asia)^ref. Formal guidelines for interpretation and comparisons of methods for detecting virus in fixed tissues have recently been published^{ref1, ref2}.


With some well-documented exceptions EBV is present in each of the tumor cells in a particular patient at all sites of disease, at presentation and at relapse. Aspects of the relationship between cases associated with the syndrome of infectious mononucleosis and tumors harboring virus have been problematic. On the one hand, those regions of the world in which HL is most consistently associated with EBV are those regions in which the syndrome of infectious mononucleosis is least common. On the other hand, regions in which infectious mononucleosis is most common have been those regions where the presence of EBV in tumor is least common. The questions that emerge are:
• is EBV only associated with HL that harbors the genome, or is the virus also associated with lymphoma in which the genome cannot be detected?
• is infectious mononucleosis associated with all HL or only with those cases in which viral gene expression can be demonstrated in tumor cells?
An association with HL that does not harbor the genome is not implausible. EBV infection of a lymphocyte might initiate tumorigenesis, perhaps leading to genetic instability or other change that ultimately renders the viral genome superfluous to the maintenance of the malignant state. Evidence has very recently been presented that EBV upregulates expression of activation-induced deaminase, the enzyme responsible for somatic hypermutation in germinal center B cells^ref. EBV need not leave any viral genetic sequences behind as a footprint. In contrast with tumor viruses whose DNA integrates into host cell DNA, loss of EBV episomes from malignancies in tissue culture is well documented in EBV tumor cell lines^ref. Some of these questions were answered in part by a population-based analysis of acute infectious mononucleosis and malignancy in Denmark and Sweden^ref. The relative risk of EBV⁺ HL was increased fourfold in patients with serologically confirmed infectious mononucleosis. There was no increase in the relative risk of EBV^- HL. The median estimated time interval from the diagnosis of mononucleosis to EBV⁺ HL was approximately 4 years. Thus infectious mononucleosis is clearly linked to EBV⁺ HL and there is no evidence to suggest that it is linked to EBV^- HL. Nonetheless, it should be noted that most patients with Hodgkin’s lymphoma have no history of documented infectious mononucleosis. Indeed, almost nothing is known of the determinants of symptomatic primary EBV infection except for evidence that infection in young adults is more likely to be symptomatic than in children. These answers are, however, still incomplete. Why EBV-associated HL accounts for highest percentage of HL in those regions where infectious mononucleosis is least common is unresolved. Similarly, there are paradoxes in terms of the association with patient age. At the extremes, children under 10 years of age and adults over the age of 70, virtually all cases are EBV-associated. However, infectious mononucleosis is most commonly associated with primary infection in the teenage or early adult years. The EBV LMP1 has been recognized as a likely contributor to tumorigenesis. Expression of the protein is transforming in immortalized murine cell lines and leads to lymphoma when expressed in B cells in a transgenic model^ref. The protein is a member of the TNFR superfamily and most closely resembles CD40. However, in contrast to CD40, LMP1 signaling is constitutively active and requires no ligand. Among the multitude of activities of LMP1, it activates NF-kB by promoting the turnover of IkBa. LMP2A also seems likely to play an important role. As noted above the tumor cells of HL do not express immunoglobulin genes. B cells that lack functional Ig would be expected to die by apoptotic mechanisms as has clearly been shown in transgenic mouse models. However, LMP2A has been shown to provide a tonic signal that mimics that associated with immunoglobulin expression so as to prevent apoptosis of such cells—at least in a murine model^ref. The role of this viral protein in preventing apoptosis in tumor cells suggests the possibility that related pathways may be targeted by small molecules for therapeutic purposes^ref. Posttransplant lymphoma and nasopharyngeal carcinoma are both EBV-associated malignancies in which monitoring of viral genome copy number in peripheral blood mononuclear cells or plasma has proven to be useful diagnostically and prognostically. In particular, plasma levels of viral DNA have been shown to be very important prognostically in nasopharyngeal carcinoma^{ref1, ref2}. Failure to clear viral DNA with therapy is indicative of early progression or relapse. Studies to determine whether EBV DNA in PBMC or plasma is similarly useful in HL are underway in the oncology cooperative groups. Viral antigens expressed in HL are commonly recognized by CD8 T cells^{ref1, ref2}. The antigens are generally not mutated in HL^ref. Most EBV-associated HL express class I MHC antigens and studies of cell lines suggest that the antigen-processing machinery is intact. Studies using adoptive cellular immunotherapy approaches have been initiated with limited success to date^ref. However, improved targeting of the T cell lines to antigens such as LMP2A actually expressed in HL holds promise as may therapeutic vaccine strategies. Is classical HL one entity or several entities? Many investigators have argued in favor of 2 or 3 "disease" models.
• EBV^- HD (40-60%) : besides the "hit and run" mechanism of EBV the etiologic role of other viruses is assumed. Hitherto unknown virus may be responsible for the peak incidence in young adults, which is a feature of HD in developed countries^ref.
• HCV (RR = 12^ref)
• HGV (RR = 1^ref-1.5^ref-10^ref)
• HIV-infected patients have higher incidence of HL^ref. In contrast to NHLs that are "AIDS-defining" malignancies, the increased incidence of HL is more subtle. The increased risk of BL and brain lymphoma in AIDS patients is hundreds- or thousands-fold, whereas the increased incidence of HL in AIDS is approximately 3- to 10-fold. A recent population-based study of HIV-HL in the San Francisco Bay area showed that 90% of HLs in HIV patients were EBV⁺, that nodular sclerosis histology was only half as common among HIV-infected patients as in the general population, and that lymphocyte-depleted disease was much more common^ref. HIV patients were also more likely to have advanced-stage disease. Whether the contribution of HIV to Hodgkin’s lymphomagenesis is simply related to generic immunodeficiency or reflects some more specific contribution of particular HIV proteins or HIV-induced immune dysregulation is not clear. However, it is worth bearing in mind that the CD4 T cell count in HIV Hodgkin’s is typically much higher than that in some other EBV-associated malignancies in HIV patients, such as brain lymphoma. Interesting evidence regarding measles has also been presented^ref.
• measles virus (MV) especially in young adults^ref : there was an increased risk of Hodgkin's disease among children exposed around birth to higher levels of measles (odds ratio for trend = 2.3)^ref. biopsies from 54.3% of patients showed a positive immunostain with at least 2 of the anti-measles antibodies used. LMP-1 immunostaining for EBV was positive in 31.1% of the patients examined. RT-PCR and ISH for measles RNA were positive in 7 and 10 of 28 patients, respectively^ref. Regression of HD after measles has been reported^{ref1, ref2, ref3}. Changes in chromosome structures observed in patient with concomitant HD and measles^ref. Report and observations on the presence of Warthin-Finkeldey cells in patients with HD^ref. Observation of cells resembling Sternberg-Reed cells in conditions other than HD^ref. Fatal subacute measles encephalitis complicating HD in an adult has been reported and considered an opportunistic infection^ref. IHC, RT-PCR and in situ hybridization studies have shown evidence of measles virus in Hodgkin’s tumor tissues in slightly more than half of patients. These include patients with and without EBV in their tumors. Any contribution to pathogenesis remains highly speculative at this point.
• mumps virus antigens were demonstrated in biopsied tissues from Hodgkin's disease patients by IFA. Impression smears from 10 lymph node and 2 spleen specimens revealed viral antigens in the nucleus, cytoplasm or both. Measles virus antigens were detected in 6 out of 7 HD tissue (lymph nodes) both in the nucleus and cytoplasm. All tissues tested for the presence of Newcastle disease virus (NDV) antigens were negative. Control tissues were obtained from patients with non-Hodgkin's lymphomas, breast cancers, adenocarcinomas and a number of other disease processes. In control tissues mumps antigens were detected in 7 out of 31 specimens and measles antigens in 9 out of 18 tissues^ref.
• despite extensive investigation, no evidence has emerged to support a role for :
• novel herpesvirus : extremely unlikely^ref
• HHV-3 / VZV^{ref1, ref2}, higher antibody titres to herpesviruses were taken to be the result of the disturbed cellular immunity^ref
• HHV-5 / CMV (33% vs. 9% of EBV^+ref) genome and antigen is localized within H/RS cells^ref
• HHV-6
• HHV-7
• HHV-8
• mumps virus antigens were demonstrated in biopsied tissues from Hodgkin's disease patients by IFA. Impression smears from 10 lymph node and 2 spleen specimens revealed viral antigens in the nucleus, cytoplasm or both. Measles virus antigens were detected in 6 out of 7 HD tissue (lymph nodes) both in the nucleus and cytoplasm. All tissues tested for the presence of Newcastle disease virus (NDV) antigens were negative. Control tissues were obtained from patients with NHL, breast cancers, adenocarcinomas and a number of other disease processes. In control tissues mumps antigens were detected in 7 out of 31 specimens and measles antigens in 9 out of 18 tissues^ref.
• rubella virus^ref
• JC virus
• adenovirus
• HTLV-1 or HTLV-2
• Bordetella pertussis^{ref1, ref2}
The ORs for lymphoma were decreased for exposure to sheep and goats (OR = 0.7), for rabbits and hare (OR = 0.7) and tetanus vaccination (OR = 0.5). Increased risk of lymphoma was associated with exposure to cattle (OR = 1.3) and immunization for tuberculosis (OR = 1.5)^ref
• intrinsic : consideration of familial HL illustrates how little we know of the fundamental pathologic processes. Although relatively rare, familial HL is well documented. Within a family’s pedigree EBV⁺ and EBV^- HL are recognized, as well as nodular sclerosis and mixed cellularity histologies. There must be several paths to HL. The relative contributions and temporal relationships of infection, immunodeficiency and other factors have yet to be answered. EBV may rescue 'crippled' (BcR^-) germinal center B cells from apoptosis^{ref1, ref2}. Identical twins of young adult HL case subjects are much more likely to develop the disease compared with fraternal twins of case subjects, suggesting a genetic determinant. IL-6 levels are increased in patients with HL and are correlated with a poor prognosis. Unaffected identical twins of case subjects (surrogate case subjects) had a 87.8% higher IL-6 level compared with matched control subjects (mean difference, +483.7 pg/mL). Analysis of the IL-6 174G>C promoter polymorphism genotypes showed that risk decreased with an increasing number of C alleles. The CC (low secreting) genotype was associated with a decreased risk of young adult Hodgkin lymphoma relative to the GG (high secreting) genotype. Risk was decreased for both nodular sclerosis and other subtypes. Persons with genetically determined lower IL-6 levels may be less susceptible to young adult HL^ref

• Jackson-Parker classification, 1944
• paragranuloma
• granuloma
• sarcoma
• Lukes-Butler-Hicks classification, 1966
• nodular lymphocytic and/or histiocytic
• diffuse lymphocytic and/or histiocytic
• nodular sclerosis
• mixed cellularity
• Rye anatomopathological classification, 1965 (Symposium sponsored by the American Cancer Society & National Cancer Institute "Obstacles to the control of Hodgkin's disease". Held at the Westchester Country Club at Rye, NY, Sept. 13-15 (1965). Cancer Research 26 (6) (1966))
• type 1 : lymphocyte predominance type
• type 2 : nodular sclerosis type
• type 3 : mixed cellularity type
• type 4 : lymphocyte depletion type
• Revised European-American Classification of Lymphoid Neoplasms (REAL) anatomopathological classification by the International Lymphoma Study Group (I.L.S.G.), 1994 :
• nodular lymphocyte predominance
• classical HL :
• lymphocyte-rich HL
• nodular sclerosis
• mixed cellularity
• lymphocyte depletion
• WHO in the recently published WHO classification of hematological malignancies, the sub-classification of HD is broadly similar to the previous Rye classification^ref. Lymphocyte-predominant HL is clearly a distinct entity from other forms of the disease as shown by immunophenotype analysis. A very high proportion of patients present with Stage IA disease and a minimalist approach to treatment may be appropriate^ref. Lymphocyte-depleted HL is now rarely diagnosed in some centers; patients who were once labelled with this entity are now mainly classified as Grade II nodular sclerosis disease or as anaplastic large cell lymphomas. With the possible exception of localized lymphocyte-predominant disease, the remaining types of HL are treated in a similar way depending upon stage^ref.
• classical Hodgkin's lymphoma (cHL) : small population (<1%) of putative malignant cells
• mononucleated Hodgkin's cells (CD99^lo)
• plurinucleated Dorothy Reed-Sternberg (RS) giant cells (Sternberg C. Ueber eine eigenartige unter dem Bilde der Pseudoleukemia verlaufende Tuberculose des lymphatischen Apparates. Zeitschr.Hlk. 19:21-90 (1898); Reed DM. On the pathological changes in Hodgkin's disease, with special reference to its relation to tuberculosis. J.Hopkins Hosp.Rev. 10:133-196 (1902)) : giant histiocytic cells, typically with polylobated nucleus (rarely binucleate with the 2 halves of the cell appearing as mirror-images of each other => owl-eye cells); the nuclei are enclosed in abundant amphophilic cytoplasm and contain prominent nucleoli surrounded by clear perinucleolar halo. Recent advances in cell isolation techniques and molecular biology has identified Ig gene rearrangements within the majority of individual HRS cells, suggesting their B cell origin^ref. These are surrounded by a large population of apparently non-malignant lymphocytes and histiocytes, whose proliferation is likely to be mediated by the wide range of cytokines and chemokines released by the HRS cells^{ref1, ref2}. HRS cells have many characteristics in common with APCs such as activated B cells and dendritic cells (DCs)^ref. Indeed, the HRS cell lines (L428, HDLM-2, and/or KM-H2) express cell surface molecules required for costimulation/proliferation of T cells (MHC class II, CD40, CD80, and CD86)^{ref1, ref2, ref3}, cell adhesion molecules involved in DC-T cell interactions (LFA-1, CD11c, and ICAM-1–3)^{ref1, ref2}, and the DC-associated molecules (CD83 and fascin)^{ref1, ref2}. They also produce inflammatory cytokines (e.g. TNF-a and TNF-b)^ref, non-inflammatory cytokines (e.g. GM-CSF, IL-5 and IL-13)^{ref1, ref2}, and chemokines (e.g. TARC)^ref, which are associated with APCs. L428 cells have been used successfully to produce monoclonal antibodies (mAb) against DC differentiation antigens such as CMRF-44^ref and CMRF-56^ref and to clone the DC-associated molecules such as DEC-205^ref and the adenosylhomocysteine hydrolase-like molecule DCAL/AHCYL-1^ref. Cell surface molecules on HRS cell might also be candidate targets for antibody-based HL immunotherapy : indeed, CD20, CD25, and CD30 reagents (markers for B cells and activated lymphocytes) have been investigated in this regard^{ref1, ref2, ref3}, but molecules more restricted to HRS cells might be preferred as targets for more specific therapeutics. HRS cells cotranscribe an mRNA containing DEC-205 and DCL-1 prior to generating the intergenically spliced mRNA to produce a DEC-205/DCL-1 fusion protein. Cotranscription and intergenic splicing is a rare event in mammalian cells, and there are only a small number of reports describing the presence of fusion mRNA. These include MDS/ EVI1^ref, galactose-1-phosphate uridylyltransferase, and IL-11R genes^ref, Prnd/Prnp^ref and P2Y1/SSF1^ref. None of these reports, however, examined whether the fusion mRNA is translated endogenously into cognate fusion protein. The genes encoding DEC-205 (LY75)^ref and DCL-1 (KIAA0022)^ref are juxtaposed within chromosome band 2q24 and are separated by only 5.4 kb. These are independent genes, because DEC-205 and DCL-1 mRNA are each expressed independently in hematopoietic cell lines. The 5'-RACE experiment mapped the DCL-1 transcription initiation site at 44 bp upstream of DCL-1 translation start codon. Both 5'-proximal promoters of DEC-205 and DCL-1 have independent promoter activity. The DEC-205 promoter may drive the cotranscription of the DEC-205 and DCL-1 genes to produce the 9.5-kb DEC-205/DCL-1 fusion mRNA. This would result from leaky termination of DEC-205 transcription, a mechanism suggested to explain the cotranscription of galactose-1-phosphate uridylyltransferase and IL-11R genes^ref. However, this seems unlikely, because the expression of DEC-205 mRNA did not correlate to that of DEC-205/DCL-1 fusion mRNA. Interestingly, all HRS cell lines tested expressed the 9.5-kb DEC-205/DCL-1 fusion mRNA, but not 4.2-kb DCL-1 mRNA, whereas other myeloid and B cell lines expressed 7.5-kb DEC-205 and/or 4.2-kb DCL-1 mRNA, suggesting that expression of DEC-205/DCL-1 fusion mRNA is highly regulated. It is intriguing to speculate that HRS cell lines express certain transcription factors that may control cotranscription of DEC-205 and DCL-1 genes. At mRNA levels, 2 DEC-205/DCL-1 fusion mRNA variants (V34-2 and V33-2) were identified different by the presence of the DEC-205 exon 34. The deletion of exon 34 appears to be the only alternative splicing that occurs naturally in DEC-205 gene transcription. The fusion junctions in the V34-2 and V33-2 DEC-205/DCL-1 fusion mRNA are in-frame, suggesting both transcripts are translated. What would be the functional difference between DEC-205 and DEC-205/DCL-1 fusion protein? Because the fusion protein contains DCL-1 CP, not DEC-205 CP, it is conceivable that DEC-205 ligand (currently unknown) to DEC-205/DCL-1 fusion protein would induce distinct signals from that binding to DEC-205^ref. RS cells could be natural hybridomas between a neoplastic precursor and reactive T or B lymphocytes at the immunological synapse. In the murine system natural hybridoma formation was observed first in 1968-9. In the #620 to 818 system a mouse leukemia virus (MLV) produced diploid lymphoma cell fused with an immune plasma cell. The tetraploid fusion product cells grew in suspension cultures and as ascites tumors in mice and continued the production of MLV particles and MLV-neutralizing antibodies. Analogy between the #620 to 818 system and the origin of RS cells is proposed. Indirect evidence suggests retroviral infection of the mononuclear HD cell which presumably is an interdigitating reticulum (IR) cell. Reactive B and T cells interact in an abnormal manner and fuse with the retrovirally infected IR cell. The fusion product cells display hyperdiploidy and a disarray of markers as IR markers are lost due to dedifferentiation (and regained upon differentiation induction) and B and/or T cell markers are gained. Conventional theories for the origin of RS cells fail to explain the great heterogeneity of their markers. Derivation of RS cells from IR cells and B and/or T lymphocytes as natural hybridomas offers plausible explanation for all the features of RS cells^ref. The formation of natural hybridomas during the course of malignant lymphoproliferative diseases was observed many times thereafter, e.g. in African Burkitt's lymphoma (BL). RS cells may be formed when retroviral antigens expressed by the mononuclear Hodgkin's cell attract reactive B and T cells, and instead of an immune attack by reactive cells, fusion with reactive cells takes place. The resulting RS cells may further fuse with other reactive cells (e.g., with 2 B cells, one expressing k, the other l light chains) or with each other, forming quadromas. RS cells appear multinucleated and hyperploid; they express the products of activated genes of the interdigitating dendritic or reticulum cell (the retrovirally infected mononuclear Hodgkin's cell) and those of reactive B and/or T cells. Thus, RS cells present themselves with a great variety of marker expression. Molecular mediators and immunoglobulins released from RS cells are responsible for the activities of proliferating polyclonal reactive cells and/or for the depletion of these cells in HD lesions. Multinucleated giant RS cells in anaplastic lymphomas and the syncytial subtype of RS cells of nodular sclerosing HD should be studied first for retro- or herpes viral antigen expressions and for fusion with reactive cells or with other RS cells^ref.


The origin of the HRS cells of cHL has been enigmatic for a long time, as they express markers of different hematopoietic lineages. Only recently the analyses of Ig and T-cell receptor loci of single HRS cells revealed that the cells represent monoclonal populations of tumor cells, and in the vast majority of cases derive from B cells and only in a few cases from T cells^{ref1, ref2, ref3, ref4, ref5}. The rearranged Ig genes are usually mutated, and in about a quarter of cases originally potentially functional Ig rearrangements have acquired obviously crippling mutations destroying the coding capacity^{ref1, ref2, ref3}. Furthermore, the pattern of SHM (the ratio of R versus S mutations in FRs) indicated that the cells were only partially selected for the expression of a functional antigen receptor during the GC reaction^{ref1, ref2}. As GC B cells with unfavorable or crippling mutations are usually quickly eliminated by apoptosis, and as only a fraction of unfavorable mutations that cause apoptosis of GC B cells are easily identifiable as crippling mutations, HRS cells as a rule may represent preapoptotic GC B cells rescued by a transforming event^{ref1, ref2}. Viable H/RS cells can be isolated from HD affected tissues by high gradient magnetic cell sorting (MACS) according to expression of CD30^ref. EBV-harboring HRS-like cells are observed regularly in infectious mononucleosis^{ref1, ref2} and occasionally also in the setting of B-CLL^{ref1, ref2}. In 2 cases of B-CLL with EBV⁺ HRS-like cells, these cells represented clonal populations of cells unrelated to the B-CLL^ref, and it may be the particular microenvironment of the lymphomas allowing expansion of EBV-harboring B cells, which are normally tightly controlled by cytotoxic T cells^{ref1, ref2}. The case presented here may indicate that in rare instances, also in lrcHL, EBV-infected B cells can become a significant population, and that these cells may even acquire an HRS-cell morphology. Increased frequencies of EBV-infected B cells unrelated to the HRS cell clone^ref are indeed often observed in cHL^{ref1, ref2}.
Aetiology : EBV⁺ (40%); impaired immune status may contribute to the development of EBV⁺ cHL in older patients and strategies aimed at boosting the immune response should be investigated in the treatment of these patients.
Pathogenesis :
• FAS mutations are rare^ref and overexpression of c-FLIP is involved in the resistance to FAS-mediated apoptosis^{ref1, ref2}
• gene silencing associated with gene promoter hypermethylation as a common cause for this aberrant phenotype in cHL-derived cell lines and also in HRS cells microdissected from primary tumors, identifying CD19, CD20, CD79a, SYK, PU.1, BOB.1, BCMA, and LCK as targets for epigenetic modification : loss of Oct2 and BOB.1/OBF.1 expression is earlier than loss of PU.1, playing a dominant role in the hierarchy of B-cell transcription factors^ref.
• CCL28, which attracts eosinophils via CCR3 and plasma cells via CCR10 and CCR3, by HRS cells defines a major subtype of cHL with frequent infiltration of eosinophils and/or plasma cells^ref.
• HRS cells also produce and secrete high amounts of CCL17 and CCL22, that attract cells expressing the CCR4 receptor, such as T_h2 lymphocyte^ref.
• HL-infiltrating lymphocytes are anergic to stimulation with some mitogens and primary as well as recall antigens but also demonstrate that these cells suppress PBMC responses^ref. They identify the presence of IL-10–secreting cells and CD4⁺25⁺ regulatory T cells. The immunosuppressive effect of the HL-infiltrating cells could be neutralized with anti–IL-10, by preventing cell-to-cell contact, and by anti–CTLA-4. The lymphocytes in HL do not produce cytokines, such as IL-2, IL-4, and IFN-g, with primary (keyhole limpet hemocyanin [KLH]) and recall (purified protein derivative [PPD]) antigens and the mitogen concanavalin A (ConA). However, in previous studies the lymphocytes were found to produce these cytokines when stimulated with phytohemagglutinin (PHA) or with phorbolester (PMA)–ionomycin. Specifically, when the CD26^– CD4 cells immediately surrounding the Reed-Sternberg cells were purified and stimulated with PMA ionomycin, they produced IL-4 and IFN-g. The potential to produce IL-4 was the reason why these cells were previously considered T_h2-like^ref. The absence of IL-2 production upon stimulation is also associated with anergy. The exact nomenclature of these cells is thus a matter of semantics. In addition to the IL-10–producing cells (T_r1), there are also TGF-b–producing cells present in the infiltrate, and these have been termed T_h3. There are variations in the populations involved in different cases. It can be concluded that, as an overall population, the infiltrating lymphocytes do not have T_h1 type functions and are probably attracted into the tissues by chemokines CCL17 and CCç22 as CCR4-expressing T_h2 cells. Although these cells do not spontaneously produce IL-2 or IL-4, they produce IL-10, despite not being fully activated, and therefore function as T_r1 cells. The major remaining question is what causes the predominance of T cells with suppressor activity in HL. It appears that HRS cells, although they have the genotype of B cells, execute a functional program that is similar to antigen-presenting cells but results in tolerance. Mechanisms include the production of immunosuppressive cytokines like IL-10, especially in EBV⁺ cases, and TGF-b, especially in nodular sclerosis cases, as well as the expression of FASL that induces cell death in FAS-expressing activated T cells, while the Reed-Sternberg cells themselves are protected by overexpression of cFLIP or infrequently by FAS mutation^ref. The relevance of these findings is that they may allow a better design of new treatment modalities. There are indications that the infiltrating cells in fact support the growth and survival of the RS cells, and therefore blocking chemokines to prevent the influx of T cells may be effective. On the other hand, blocking of the immunosuppressive signals, such as IL-10 and TGF-b cytokines, or the removal of the suppressor regulatory T cells may enhance the effect of adoptive transfer of cytotoxic T cells^ref. A marker of regulatory T-cells, LAG-3 is strongly expressed on infiltrating lymphocytes present in proximity to HRS cells. Circulating regulatory T-cells (CD4⁺25^hi45RO^hi, CD4⁺CTLA4^hi and CD4⁺LAG-3^hi) were elevated in HL patients with active disease when compared to remission. Longitudinal profiling of EBV-specific CD8⁺ T-cell responses in 94 HL patients revealed a selective loss of interferon-gamma expression by CD8⁺ T-cells specific for latent membrane proteins (LMP) 1 and 2, irrespective of EBV tissue status. Intra-tumoral LAG-3 expression was associated with EBV tissue positivity, whereas FOXP3 was linked with neither LAG-3 or EBV tissue status. The level of LAG-3 and FOXP3 expression on the tumor- infiltrating lymphocytes was co-incident with impairment of LMP1/2-specific T-cell function. In vitro pre- exposure of peripheral blood mononuclear cells to HRS cell-line supernatant significantly increased the expansion of regulatory T-cells and suppressed LMP- specific T-cell responses. Deletion of CD4⁺ LAG-3⁺ T- cells enhanced LMP-specific immunity. These findings indicate a pivotal role for regulatory T-cells and LAG-3 in the suppression of EBV-specific cell-mediated immunity in HL^ref.
• HRS-specific genes include GATA-3, ABF-1, EAR3, and NRF3^ref
• as BCR represents the major survival signaling pathway in normal B-cells, the global down-regulation of its components in HRS cells seems to be contradictory, unless the acquisition of other survival programs (such as constitutive NF–kB activation)^ref, would obviate the necessity of the normal B-cell gene program and thus initiate a selection process against maintaining such a program. In this scenario, it is tempting to speculate that the silencing of the expression of the BCR-related genes is a benefit for HRS cells. Given the described roles of several BCR signaling components in regulation not only of B-cell proliferation but also of B-cell apoptosis, silencing the expression of these genes might actually be a selective advantage for HRS. Different reports have also shown that the levels of expression of BCR-signaling genes could be opposite of the levels of NF-kB activation, as is the case of PMLBCL^ref, a tumor closely related to cHL^ref. The lost B-lineage identity in HRS cells (as seen by immunophenotype and gene expression profiles^{ref1, ref2, ref3}) may explain their survival without BCR expression and reflect a fundamental defect in maintaining the B-cell differentiation state in HRS cells, which is likely caused by a novel, yet unknown, pathogenic mechanism. The B cell–specific transcription factor program was disrupted by overexpression of the HLH proteins ABF-1 and ID2. Both factors antagonized the function of the B cell–determining transcription factor E2A. As a result, expression of genes specific to B cells was lost and expression of genes not normally associated with the B lineage was upregulated. These data demonstrate the plasticity of mature human lymphoid cells and offer an explanation for the unique cHL phenotype^ref.
Laboratory examinations :
• immunophenotype : CD15⁺19^-20^-22^-30 / Ki-1 Ag⁺40^-45^-99^lo138^{+ref1, ref2, ref3}sIg^-. On the other hand, inappropriate lineage marker expression of dendritic cells, monocytes, or macrophages can be found in HRS cells^ref. Reactive CD4⁺40L⁺57^-- lymphocytes surrounding HRS cells
• cytomorphology : largePU.1^-refBCL6^{-ref1, ref2}Oct2^-BOB1/OBF.1^{- ref1, ref2}. Pax-5^+ref
• histology :
• nodular sclerosis (NS) HL (65-75%)
• grade 1 : hypocellulated
• grade 2 : cellulated
Epidemiology : bimodal peaks, developed countries with middle-high social status
Symptoms & signs : 40-60% diagnosed in stage I-II; mediastinum (> 60%), bone marow (5-10%)
Laboratory examinations :
• cytomorphology : RS cells are in the form of lacunar cells (large, irregular, single contracted nucleus with small nucleoli surrounded by an ample, pale-staining cytoplasm retracted during formalin fixation (possibly spanned by a few shreds of cytoplasm) enclosed in a sharply defined cell membrane)
• immunophenotype : CD15⁺20^-30⁺45^-BcR L k or l chain^+(sometimes)

..., and birifrangent (under polarized light microscope) bands of collagen divide the lymphoid tissue into nodules; there are varying numbers of lymphocytes and inflammatory cells such as histiocytes, eosinophils (causing prurigo), small lymphocytes and plasma cells. This type is most common in young women diagnosed at stage I  or II (60%) and often has a low grade of malignancy, usually affecting lower cervical, supraclavicular and mediastinic lymph nodes
• syncytial variant : sheets of very atypical Reed-Sternberg cells proliferate in the midst of the nodule. In some studies it has a slightly worse prognosis than cases of nodular sclerosis lacking this feature.
• Bennett II
• diffuse patterns
• lymphocyte depletion classical HL (LD-CHL) / Hodgkin's sarcoma (1-5%) : low number of lymphocytes and an abundance of Reed-Sternberg cells with fibrosis; it is the most aggressive of the 3 diffuse types of Hodgkin's disease (prognosis is 10-39 months survival after chemotherapy).
• diffuse fibrosis : hypocellulated, rare RS cells, abundant connective tissue and fibrinoid material
• reticular form : minimal reactive component, lack of connective tissue, pleomorphic RS cells (eosinophilic and bizarre nucleoli)
Epidemiology : more common in people aged 50-60
Symptoms & signs : diagnosed at stage III/IV; retroperitoneal, bone marrow (50-75%)
• mixed cellularity (MC) HL (25-30%) : intermediate between the lymphocyte predominance and lymphocyte depletion types; RS cells are plentiful (mirror cells) and there are more inflammatory cells, such as eosinophils, histiocytes, neutrophils, small lymphocytes and plasma cells, than in the lymphocyte predominance type.

Epidemiology : advanced age, poor countries, low social status
Symptoms & signs : < 25% diagnosed in stage I-II; usually diagnosed at stage III or IV (50%) => worse prognosis; mediastinum (15-20%), bone marrow (20-25%)
• lymphocyte-rich classical HL (LR-CHL) (provisional entity), first described by Lennert and Mohri in 1974
• nodular lymphocyte-predominant Hodgkin's lymphoma (NLPHL) / paragranuloma (5-6%) : the neoplastic cells are atypical lymphocytic and histiocytic cells (L&H). The expression of several B-cell markers suggested a B-cell origin, and single-cell studies indeed revealed that the L&H cells carried rearranged Ig genes^{ref1, ref2, ref3, ref4}. Although the Ig rearrangements in both cHL and lpHL are mutated, the mutation patterns are different. In contrast to cHL, in most lpHL cases analyzed intraclonal diversity was observed and the rearranged Ig genes carried no crippling mutations and were selected for expression of a functional antigen receptor^{ref1, ref2, ref3}. These findings indicate that the L&H cells of lpHL are derived from mutating GC B cells.

Epidemiology : most patients are males under age 35 diagnosed at stage I or II (80%) and living in developed countries with middle-high social status
Aetiology : EBV^-
Pathogenesis : unexpected expression of IgD in 27% of cases. IgD is usually coexpressed with IgM in naive B cells but can also be seen as IgD-only in centroblasts (CD38⁺) or memory B cells (CD27⁺). Clinically, the IgD⁺ cases present at a younger median age (21 vs. 44 years) and have a striking male predominance (male-to-female ratio, 23:1 vs. 1.5:1). Cervical lymph nodes were more frequently involved (56% vs. 18.2%). L&H cells were localized in a predominantly extrafollicular distribution in the majority of IgD⁺ cases (69%). The IgD-positive cases did not coexpress IgM or CD27 (a marker associated with memory B cells), and nearly all (93%) were weakly positive for CD38, supporting a GC derivation. The expression of Bcl-6, BOB.1, Oct2, and SWAP-70 was similar in the 2 groups. However, PU.1 expression was seen in 60% of the IgD⁺ cases in contrast to 86% of the IgD^- cases. The absence of PU.1 staining correlated with more L&H cells in an extrafollicular distribution, weakening the use of this marker in the differential diagnosis with T-cell rich/histiocyte rich B-cell lymphomas. To study IgD expression in "de-novo" T-cell rich/histiocyte rich B-cell lymphomas, we analyzed 20 cases and all but 1 were negative. In conclusion, cases of IgD⁺ NLPHL do not differ from IgD^- cases regarding cellular derivation and most other immunophenotypic characteristics. However, IgD⁺ NLPHL exhibits distinctive clinical features, and more often involves the interfollicular region in a background relatively rich in T cells. IgD⁺ may represent an additional useful marker in the diagnosis of NLPHL^ref
Symptoms & signs : mediastinum (5%), bone marrow (< 5%)
Laboratory examinations :
• histology : diffuse to slightly nodular infiltrate with abundant mature lymphocytes and varying numbers of benign histiocytes, eosinophils, neutrophils and small T cells resembling GC T cells (CD57⁺BCL6⁺)^ref; there are few neoplastic cells and the degree of malignancy is low
• immunophenotype : CD15^-19⁺20⁺22⁺30^-40⁺45⁺w75⁺79a⁺138^- EMA⁺ BcR L k or l chain^+(sometimes). Reactive CD4⁺40L^-57⁺ lymphocytes that form rosettes around L&H cells
• cytomorphology : popcorn cells (multilobed nucleus that resembles an exploded popcorn kernel), BCL6^{+ref1, ref2}PU.1^-refOct2⁺BOB1/OBF.1^{+ref1, ref2}
Prognosis : 3-5% develop diffuse large B-cell lymphoma (DLBCL)

• unclassifiable HL

• painless, progressive enlargement of superficial lymph nodes
• lymph nodes and spleen (90%)
• laterocervical and supraclavear lymph nodes (70%)
• chest / mediastinum (45%) (including bulky mediastinal adenopathy if > 2/3 of maximal transverse chest diameter)
• paraaortic lymph nodes (35%)
• spleen (13%)
• axillary (20%)
• inguinal (10%)
• extranodal (10%)
• liver (10%)
• lung (6%)
• skeletal (5%; 15% overall)
• other (10%)
• primary gastrointestinal Hodgkin's disease (extremely uncommon)
Kaplan-Rosenberg contiguity theory : lymphogenous and hematogenous spreading
=>
• perineal and/or lower limb edema due to paraortic lymphadenomegaly obstructig inferior vena cava
• obstructive jaundice
• acute renal failure due to ureteral obstruction by retroperitoneal lymphadenomegaly
• spinal cord compression by infiltration of epidural spaces
• dermal and subcutaneous nodules
• systemic symptoms (40%) : anorexia, fatigue, weight loss (> 10% in the 6 months before diagnosis), Pel-Ebstein fever, pruritus, night sweats, and anemia

• Ann Arbor clinical staging (cS), Michigan, USA, 1970^ref :
• I : only 1 lymph node region (I) or 1 extranodal zone/organ (I_E) : every organ other than lymph nodes, spleen, thymus, Waldeyer's ring, appendix, Peyer's plaques) is involved. 10-yr OS = 79-90%
• II : 2 or more lymph node regions are involved on the same side of the diaphragm or local invasion of one extranodal organ or region (II_E). 10-yr OS = 74-80%
• III : different lymph node regions are involved on both sides of the diaphragm or local invasion of one extranodal organ or region (III_E) or of the spleen (III_S), or both (III_ES). 10-yr OS = 55-60%
• III₁A : when among subdiaphragmatic lymph nodes only high abdominal ones are involved, expecially splenic hilar, celiac and portal hilar, in addition to spleen
• III₂A : when among subdiaphragmatic lymph nodes only paraortic, iliac and mesenteric ones are involved, with or without involvement of high abdominal ones
• IV : diffuse or generalized in one or more extranodal organs, with or without any lymph node involvement (metastasis in bone marrow, liver or lungs (no in CNS)). 10-yr OS = 35-40%
... and attributes :
• A : no general symptoms
• B : general symptoms (weight loss > 10% in the 6 months before diagnosis, night sweats, chill-less fever > 38°C (oral) not due to infections)
Sites are named by capital letters : N (lymph nodes), L (lung), O (bone), H (liver), M (bone marrow), D (skin), S (spleen), P (pleura), K (kidney)
Clinical course :
• localized disease : I-IIA
• advanced disease : IIB-IV
• Cotswolds criteria, UK, 1989^ref :
• stage I : only 1 lymph node (I) or extranodal site (tonsilla, tonsilla lingualis, spleen, thymus) (I_E) is involved
• stage II : pathology in 2 or more sites on the same side of the diaphragm. The number of involved sites must be registered, e.g. II3
• stage III : pathology in lymph node regions on both sides of the diaphragm
• stage III1 : with or without lymph nodes at the hilus of the spleen, of the liver or in the coeliaca group
• stage III2 : with para-aortic, iliac and mesenteric nodes
• stage IV : one or more extranodal zone is involved, except those labelled as E
• systemic symptomatology
• A : no general symptoms
• B : general symptoms (fever, night sweats, weight loss (pruritus is not considered)
• X : bulky disease (> 10 cm large or broadening up to > 1/3) : if mediastinal lymphadenitis => dyspnea
• E : only one extranodal region is involved, contiguous to a normal nodal region

• CBC : autoimmune haemolytic anaemia (AIHA), eosinophilia
• sideropenia (sideremia, transferrin, ferritin), hypercupremia
• b₂-microglobulin, LDH, fibrinogen, creatinine, uricemia, bilirubin, SGOT, SGPT, g-GT, alkaline phosphatase, total serum proteins, serum protein electrophoresis with dosage of IgG, IgA, and IgM
• increased ESR, a₂-globulins and CRP
• bone marrow trephine biopsy (BMTB)(positive in 15%) : it is not necessary in clinical stage I-IIA. However, bilateral BMTB is recommended in the presence of B symptoms also in patients with localized stage disease^ref.
• echography of abdomen and soft tissues (neck, armpits, groin)
• whole-body CT (eventually partially replaced by chest X-rays)

• lymph node biopsy (cervical > mediastinoscopy / mediastinotomy) : FNAB
• ⁶⁷Ga-citrate scintigraphy
• MRI
• bipedal or pedal lymphangiography has no place in the evaluation of HD and is no longer practiced
• ¹⁸FDG-PET has a number of potential advantages for the hematologist-oncologist in refining and improving the management of HL.
• staging : Hodgkin’s lymphoma is generally treated according to stage and risk profile; therefore, pretherapeutic staging provides the basis for different treatment strategies such as RT, chemotherapy or a combination of both. Owing to the increasing use of chemotherapy at early stages and the result of the EORTC H6-F study, staging laparotomy has disappeared as a routine staging procedure. Staging of Hodgkin’s lymphoma was, until recently, mainly based on computed tomography (CT). Although structural imaging provides exquisite anatomic detail, it requires perturbation or enlargement of anatomical structure to suggest tumor. Minimally affected lymph nodes of normal size or parenchymal involvement with insufficient contrast to surrounding tissue may therefore be missed, whereas enlarged inflammatory nodes are erroneously seen as tumor deposits. With regard to bone marrow involvement, which is expected in 5–15% of patients with untreated Hodgkin’s lymphoma, iliac crest biopsy is performed routinely, but due to patchy involvement lesions may be frequently missed. Recently, metabolic imaging with PET has been increasingly used in the management of lymphoma patients. Since PET relies on the detection of metabolic alterations observed in cancer cells, this examination yields data that are independent of associated structural characteristics. Furthermore, the ability to perform whole body imaging within one examination without increasing the radiation burden makes PET an ideal technique to "screen" patients for cancer deposits. The most frequently used tracer is the glucose analogue FDG. The use of FDG for in vivo cancer imaging is based upon the higher rate of glucose metabolism of cancer cells compared with nonmalignant tissue. With the exception of small lymphocytic and MALT lymphomas, most lymphomas, including Hodgkin’s lymphoma, exhibit moderate to high FDG uptake^ref. Several studies have investigated the role of FDG-PET for the initial staging of lymphoma^ref. The majority of these studies compared the performances of PET with other imaging modalities. Studies were often retrospective and included a mix of NHL and Hodgkin’s lymphoma patients without separately analyzing for these histologic subgroups. Another drawback is the lack of a true gold standard against which new imaging modalities can be compared. Discordant findings between scanning techniques are uncommonly evaluated with biopsy confirmation, and the alternative approaches of follow-up of therapy, or provision of treatment based on the results of one of the tests, have associated limitations as both false positive and negative findings are observed. Compared with gallium scintigraphy, FDG-PET appears to have advantages that include inherent superior resolution, higher sensitivity (especially in the abdomen and bone), lower radiation burden (10 mSv/PET versus 44 mSv/gallium scintigraphy) and a shorter examination time (2 hours for PET versus 3 days for gallium scintigraphy)^{ref1, ref2} FDG-PET was also found to be more sensitive and specific than bone scintigraphy for the detection of cortical bone involvement^ref and complementary to bone marrow biopsy for detection of marrow involvement distant from the biopsy site^ref. Most reports have focused on comparisons of PET with CT^ref. In most cases, PET was found to be more sensitive for detecting of both nodal (e.g., small sized nodes) and extra-nodal (especially spleen and bone) involvement, but PET-negative, CT-positive lesions do occur in a small number of cases. High FDG uptake in brown fat tissue or muscle can hamper the interpretation of the head and neck and mediastinal regions. Moreover, physiological uptake in gut and the renal collecting system can obscure evaluation of lymphoma in adjacent nodal sites. Therefore, optimum use of FDG-PET is likely in combination with CT. Combined use of PET-CT can improve accuracy by increasing the certainty of diagnosis in those difficult regions^ref. Incorporating PET in the initial staging in lymphomas results in upstaging or downstaging in 10–20% of patients, but the impact on treatment management is less obvious. Naumann et al^ref analyzed the potential impact of PET staging on therapy decision in 88 patients with Hodgkin’s lymphoma. Concordant findings between PET and CT were found in 70/88 patients (80%). In 11 patients (13%), PET detected additional sites, which would have resulted in treatment intensification in 9 of them, all with early stage disease. Focusing on the patients with stage IA-IIB disease only (n = 44), treatment would have been intensified in 20%. Compared to conventional diagnostics, PET downstaged 7 patients (8%) but this was only correct in 1 patient (inflammatory enlarged cervical node). False negative PET findings would have erroneously led to a minimization of therapy in 6 patients (7%). Therefore, FDG-PET should not be used instead of but in combination with conventional diagnostics.
• evaluation of residual masses after treatment : approximately two-thirds of patients with Hodgkin’s lymphoma will have a residual mass seen with standard imaging tests at the end of treatment, but only 20% of these patients will eventually relapse. The principal imaging modality for post-treatment follow-up is CT, but these scans are not able to accurately differentiate between a benign fibrotic mass and residual tumor. Early identification or prediction of patients who have not been cured with their primary treatment is important, since better outcomes with further treatment might be expected when this therapy is given at an earlier stage and with a lower tumor burden. It is common practice to consider RT to a residual mass of uncertain significance. However, late morbidities that include cardiovascular toxicity and secondary malignancies are potential risks that challenge this "standard" use of RT. Several recent reports have shown the effectiveness of FDG-PET in the evaluation of residual disease at the end of treatment, including studies assessing patients with HL^{ref1, ref2, ref3, ref4, ref5, ref6, ref7, ref8, ref9}. A high negative predictive value (NPV) of FDG-PET (81%–100%) has been consistently reported by most studies, clearly showing the ability of PET to identify patients with an excellent prognosis. Relapses are infrequent and occur rarely within the first year after completing treatment, and therefore probably reflect low tumor burdens that are below the limit of PET detection. Since a substantial number of patients received additional RT after a negative PET scan, reported progression-free survivals (PFS) and NPVs may represent overestimations. The question of whether, after first-line chemotherapy, RT can be omitted in patients with a negative PET scan is therefore still unanswered. Prospective randomized trials are needed to compare the PFS, overall survival (OS) and long-term complications observed in patients with a negative PET after chemotherapy who receive no further therapy or standard RT as planned at the initiation of treatment. Value of fluorodeoxyglucose–positron emission tomography (FDG-PET) in the detection of residual disease after treatment in HD patients :

	number	negative predictive value (NPV)	positive predictive value (PPV)	mean follow-up (FU) (range)	PFS@ 1 year
					PET– (complete metabolic response)	PET+ (residual disease on PET)
Hueltenschmidtref	63	98%	86%	24 (3–41)	ns	ns
Spaepenref	60	91%	100%	32 (13–50)	95%	40%
Dittmanref	24	94%	88%	> 6	ns	ns
Naumannref	43	100%	25%	35 (15–58)	100%	75%
Weihrauchref	29	84%	60%	28 (16–68)	95%	40%
De Witref	37	96%	46%	26 (2–34)	100%	75%
Lavelyref	20	81%	ns	36 (9–75)	ns	ns
Guayref	48	92%	92%	ns	100%	45%
Jerusalemref	36	94%	100%	ns	ns	ns

In contrast to the NPV, the positive predictive value (PPV) of PET is more variable (25–100%). We have observed that, for several reasons, false positive rates decrease with increasing experience in evaluating residual masses. First, the timing of PET scanning is crucial. If done immediately after completing RT, inflammatory changes can result in false positive interpretations. Therefore, it is better to perform PET before RT or to wait at least 3 months after completing RT. Second, patients with Hodgkin’s lymphoma are often young and develop thymic hyperplasia at the end of treatment. This produces a typical pattern on FDG-PET with a butterfly-shaped configuration with moderate and homogeneous FDG uptake, whereas residual lymphoma is associated with a more intense and focal pattern^ref. Thirdly, intense FDG uptake in muscle and brown fat tissue may be seen in lean and young patients and can hamper the detection of residual nodes after treatment (Dobert N, Menzel C, Hamscho N, et al. Atypical thoracic and supraclavicular FDG-uptake in patients with Hodgkin’s and non-Hodgkin’s lymphoma. Q J Nucl Med. 2004;48:33–38); combined PET-CT images are often necessary to resolve these appearances. Finally, inflammatory lesions are known to cause false positive PET findings and occur more frequently after chemotherapy. Correlation of PET findings with pretreatment scans (a new lesion in a previously noninvolved region is rarely lymphoma), clinical history or other imaging modalities can help to identify these lesions. When PET images are interpreted in correlation with clinical history and CT by radiologists/nuclear medicine physicians with specific expertise in PET, the PPV of PET in patients with Hodgkin’s lymphoma is probably equivalent to that observed in NHL (> 80%) and residual positivity is highly suggestive of residual lymphoma for which additional treatment should be considered. In equivocal cases close follow-up or additional diagnostic procedures may be warranted to reduce risks of giving additional treatments that are based on false-positive results.
• early response monitoring for risk stratification ("interim PET")^ref : since treatments that are more aggressive, but also more toxic, are available, there is a growing interest in the use of risk-directed approaches to utilize prognostic factors that predict for relapse. The International Prognostic Index (IPI) for HL^ref summarizes different prognostic clinical factors at presentation and has become an established parameter for risk stratification. The clinical features incorporated in the IPI reflect the biologic heterogeneity of the disease. However, the duration of a complete remission (CR) and other long-term outcomes might be more affected by the sensitivity of the tumor to chemotherapy than by the prognostic factors seen at presentation. Reliable predictions of outcome early in the treatment phase could lead to more immediate changes of therapy that might improve outcomes, including survival. Morphological imaging modalities, as a criterion for early response monitoring, are inefficient at differentiating responders from non-responders, in part because several courses of chemotherapy are necessary before effectiveness can be reliably determined. Using CT findings as a criterion for early response may label an unacceptable number of patients as poor responders and expose them to more aggressive or experimental therapies, even if these patients could achieve durable complete responses with standard chemotherapy. Promising results with FDG-PET can be obtained when evaluating treatment response. Because glucose provides the primary source of carbons for the de novo synthesis of nucleic acids, lipids and amino acids, FDG uptake is closely related to the number and proliferation capacity of viable cells. Treatment-induced changes resulting in tumor cell death or growth arrest reduce FDG uptake, making this a sensitive and early marker of response^ref. Romer et al^ref described a rapid decrease of FDG-uptake in patients with NHL as early as 7 days after commencing treatment. However, FDG-uptake at 42 days correlated better with long-term outcomes; early FDG reduction probably reflects initial chemosensitivity of the tumor whereas results of later evaluations are more related to the detection of resistant clones. Since that initial description, several studies have correlated PET response during treatment with final outcome, either focusing on the value of PET during initial induction treatment^{ref1, ref2, ref3, ref4, ref5, ref6} or prior to high-dose therapy and stem cell transplantation (HDT/SCT)^{ref1, ref2, ref3, ref4, ref5}.
• early response assessment of first-line induction chemotherapy : persistent PET positivity observed after a few cycles of chemotherapy is associated with a high probability of relapse at the end of treatment (PPV 67%–100%). To date, experience has been almost exclusively gained in patients with aggressive NHL. In the largest prospective study, by Spaepen et al^ref, evaluating 70 patients with aggressive NHL, 33 patients showed persistent abnormal FDG uptake after 3–4 cycles of doxorubicin containing first-line therapy and none of these patients achieved a durable CR (median PFS, 45 days). Of the 37 patients with a negative mid-treatment PET, only 6 relapsed with a median PFS of 301 days (P < 0.00001). In a multivariate analysis, FDG-PET at mid-treatment was a stronger predictor for PFS (P < 0.0000001) and OS (P < 0.000009) than the IPI (P < 0.58 and P < 0.03, respectively). Preliminary data in Hodgkin’s lymphoma by Mikhaeel et al^ref show similar results: all 6 patients with persistent disease on PET relapsed compared to only 2 out of 26 patients with a negative PET scan mid-treatment. Prospective trials are now required to establish the clinical role of PET in this setting by comparing overall survival after randomizing patients with positive mid-treatment FDG-PET findings to either continue standard induction therapy or to switch to a more aggressive approach

	number	histology	treatment	timing PET cycles	positive predictive value (PPV) for relapse	mean follow-up (FU) (months)	PFS@ 1 year
							PET+ (residual disease on PET)	PET– (complete metabolic response)
Jerusalemref	28	NHL	first-line relapse	2–5	100%	28	20%	81%
Mikhaeelref	23	NHL	first-line	2–4	87%	30	12%	100%
Mikhaeelref	32	HD	first-line	2–4	100%	36	0%	92%
Kostakogluref	30	NHL/HD	first-line relapse	1	87%	19	13%	87%
Spaepenref	70	NHL	first-line	3-4	100%	36	10%	92%
Zijlstraref	26	NHL	first-line	2	75%	25	42%	80%

• prognostic value of FDG-PET before HDT/SCT : improvements in therapy may mean that patients with nonresponding or relapsing disease represent a cohort that has an even more unfavorable prognosis. Currently, many centers consider high-dose therapy with autologous stem cell transplantation as the treatment of choice for these poor prognosis lymphoma patients. The most important prognostic factors to predict favorable outcome after HDT/SCT are the duration of remission prior to progressive disease and the chemosensitivity of the tumor to salvage therapy administered prior to SCT. Since FDG-PET has become a potential tool to differentiate between responders and non-responders early during chemotherapy, several groups have investigated the value of [¹⁸F]FDG-PET to identify patients who would benefit from this aggressive treatment. Again, high PPVs with short PFS are recorded in patients with persistent disease on PET. Co-existing inflammatory disease is more frequently seen in this population and can cause false-positive PET results. Correlations of PET, clinical and morphological imaging data are therefore essential. Superior PPVs are obtained if PET is performed just prior to transplantation (> 87%) compared with those performed early during the administration of salvage therapy (Schot et al^ref, PPV = 65%). This is not surprising since resistant clones can only become apparent when the sensitive ones are killed. These findings are confirmed by quantitative analyses: only a major decrease in the amount of FDG uptake and not the reduction in metabolic volume is predictive for favorable outcome. Further studies are necessary to define the optimal timing of PET and response criteria before this technique can be used as a standard practice to determine patient eligibility for HDT/SCT. For post-treatment evaluation, especially if a residual mass is present, PET has become a standard procedure in routine clinical practice and has replaced gallium scintigraphy as an adjunct to CT. In cases where, after completing first-line treatment, abnormal FDG-uptake is seen in initially involved sites and there is a low suspicion of co-existing inflammation, strong consideration for providing alternative therapy should be given. In HL patients with stage III or IV disease, negative PET results do not exclude minimal residual disease and/or the risk of late relapse. These patients might benefit from repeated follow-up scans. Patients with early-stage Hodgkin’s lymphoma and a negative FDG-PET scan after therapy are considered as CR and follow-up scanning is indicated only if recurrent disease is suspected. The increasing use of integrated PET-CT systems requires systematic evaluation, including assessment of the radiation burden associated with repetitive combined imaging studies. For prognostic determination in the early phases of therapy, there are promising data for the predictive role of FDG-PET, but larger patient populations and longer follow-ups are necessary for confirmation. As current studies are extended, data regarding the timing of the interim scan, definition of PET response criteria, and utility in tailoring RT, stem cell transplantation and radio-immunotherapy will become available. These assessments of utility, potentially supported with the results of economic evaluations, will inform the process to determine new standards of practice.
 

	number	histology	indication  SCT	timing PET		positive predictive value (PPV) for relapse	negative predictive value (NPV)	PFS@ 2 year estimated from Kaplan Meier plots
								PET response	PET non-response
Bechererref	16	HD/NHL	not spec	prior to SCT	no or minimal residual disease	87%	87%	88%	18%
Cremeriusref	22	NHL	first-line	prior	> 25% decrease to SCT	86%	67%	72%	28%
Filmontref	20	HD/NHL	first	prior relapse	no residual disease to SCT	92%	87%	88%	8%
Schotref	46	HD/NHL	first	mid relapse	no residual disease induction	65%	67%	62%	38%
Spaepenref	60	HD/NHL	first	prior relapse	no residual disease to SCT	87%	90%	100%	24%

• staging laparotomy with eventual liver biopsy
• splenectomy increases risk of secondary leukemia

• treatment of localized disease :
• external beam radiotherapy (EBRT) (highly radiosensitive : 40-45 Gy in 4 weeks) : extent of radiation fields : for those patients in whom radiotherapy alone is employed, the extent of the radiation field is critical in determining the relapse rate but probably not the overall survival. Specht and colleagues in the International Hodgkin's Disease Collaborative Group carried out a meta-analysis of 8 randomized trials involving 1,974 patients who received more or less extended radiation fields^ref. The use of more extensive radiation fields was associated with the reduction in the actuarial relapse rate at 10 years from 43% to 31% (P < 0.00001), but the overall survival at 10 years was 77% regardless of the extent of the radiation field. Selected series of patients with localized Hodgkin's disease treated with different radiation fields :

radiation field	center	patients	no. of patients	DFS	survival	years (time point for DFS and overall survival)
involved field irradiation	MD Anderson (7)	pathological stage (laparotomy-staged) (PS) I and II (A and B)	87	54%	-	10
		clinical stage (CS) I and II (A and B)	133	35%	-	10
	British National Lymphoma Investigation (BNLI) (3)	PS I and IIA	107	54%	81%	10
mantle field irradiation	BNLI (3)	PS I and IIA	212	57%	79%	10
	Melbourne (8)	CS I and II (A and B)	64	46%	89%	5
		PS I and II (A and B)	66	67%	90%	5
	EORTC (5)	CS I and II (A and B)	152	38%	60%	12
	Toronto (4)	CS I and IIA	121	62%	-	10
extended field irradiation mantle	Boston (9)	PS I and IIA	108	74%	89%	5
	Chicago (10)	PS I and IIA	92	77%	71%	10
	EORTC (5)	CS I and II (A and B)	108	63%	80%	7
subtotal lymphoid irradiation (STLI) / subtotal nodal irradiation (STNI)/total lymphoid irradiation (TLI) / total nodal irradiation (TNI)	Stanford (11)	PS I and II (A and B)	109	77%	84%	10
	Denmark (12)	PS I and II (A and B)	133	90%	90%	7

Side effects : radiation-induced breast and lung cancers
More extensive radiotherapy fields or the addition of chemotherapy to radiotherapy in the initial treatment of early-stage Hodgkin's disease had a large effect on disease control, but only a small effect on overall survival. Recurrences could be prevented by more extensive radiotherapy or by additional chemotherapy. However, if chemotherapy had not been given initially, recurrences were generally salvageable by re-treatment with chemotherapy. Hence, less intensive primary treatment--particularly a reduction in radiotherapy fields--appears to achieve similar survival rates as more intensive treatment, although more randomized evidence is needed to confirm this^ref. Patients who relapse are generally responsive to chemotherapy.
• combined modality therapy : many centers have explored the use of combination chemotherapy + extended field irradiation to treat localized disease and this undoubtedly reduces the relapse rate compared to the use of radiotherapy alone. In the EORTC H1 trial the administration of weekly vincristine for 2 years after the completion of regional radiotherapy for CS I and II (A and B) disease markedly improved relapse-free survival (61% vs 38% at 12 years; p < 0.001) and there was a trend to improved overall survival (70% vs 60%; p = 0.08)^ref. Most trials have not, however, demonstrated a survival advantage. The International Hodgkin's Disease Collaborative Group performed an analysis of 13 trials involving the randomization of combined modality treatment against radiotherapy alone. The addition of chemotherapy halved the 10-year risk of failure from 32.7% to 15.8% (p = 0.00001), but the improvement in survival was insignificant (79.4% to 76.5%)^{ref1, ref2}. A trial from a French co-operative group of combined modality therapy in CS I, IIA and IIIA disease suggested that in the context of combined modality treatment, more limited radiation fields were fully efficacious and that 3 cycles of MOPP were as effective as 6 cycles^ref. A number of other studies have addressed the use of fewer cycles of chemotherapy or the use of less intensive chemotherapy regimens with the aim of reducing the undoubted toxicity of combined modality therapy. At Stanford subtotal nodal irradiation (STNI) was compared with involved field (IF) radiation plus VBM (vinblastine, bleomycin, methotrexate) chemotherapy (non-sterilizing and low leukemogenicity) in laparotomy-staged patients with localized disease^ref. There was a highly significant improvement in disease-free survival (95% vs 70%) but again no survival difference. A further study using 6 weeks of VBM in a different schedule, however, revealed considerable pulmonary toxicity attributed to the bleomycin given before the mediastinal radiation^ref. In Manchester a month's course of VAPECB (vincristine, doxorubicin, prednisolone, etoposide, cyclophosphamide and bleomycin), another non-sterilizing regimen was added to radiation therapy and compared with radiation alone in a randomized phase II study^{refRadford JA, 66}. The progression-free survival at 4 years was 90% with the combined modality, compared to only 64% with radiation alone.
• chemotherapy alone : at the National Cancer Institute patients with PS IB, IIA, IIB and IIA1 disease were randomized to STNI or MOPP alone^ref. The projected 10-year disease-free survival of patients randomized to receive radiation was 60% compared to 86% in those who received MOPP (p = 0.009). There was also a borderline significant survival benefit for the MOPP recipients but this was mainly seen in patients with bulky mediastinal disease. In contrast to these excellent results with MOPP an Italian study in PS I and II disease found similar rates of freedom from progression but reduced survival in the MOPP recipients due to a frequent failure of salvage therapy after a relapse from MOPP therapy^ref.
• first-line chemotherapy :
• ABVD
• hybrid MOPP/ABVD
• Stanford V
• salvage therapy :
• IEV
• IGEV
HL is an uncommon form of cancer. In Canada, a country of approximately 32 million people, the most recent available annual statistics (from 2000^ref) show that 134,413 people were diagnosed with cancer and 62,672 deaths were attributed to this disease. The most common hematologic neoplasm was NHL, with an incidence of 5444 new cases and 2537 deaths. In contrast, a new diagnosis of Hodgkin’s lymphoma was made in 811 people and 128 deaths observed. These data exemplify the success of current therapies that have resulted in high expectations of cure for patients with HL, but also demonstrate the nature of future challenges; strategies are needed to identify and provide successful therapy to the 15%–20% of patients who are not cured, and for the more than 80% of patients who have had their cancer successfully eradicated, long-term threats to quality of life and survival need to be reduced. Given the uncommon nature of Hodgkin’s lymphoma, evaluation of interventions to improve long-term outcomes will require international collaborations and, by definition, long periods of follow-up. For patients with limited-stage Hodgkin’s lymphoma, the development of successful therapies that control the malignancy makes evaluation of the competing objectives to eradicate the cancer while reducing the risks of long-term treatment-related toxicities particularly important. This balance has evolved even over the past 15 years. In 1989, an international collaboration of single institutions and cooperative groups led to the Paris International Workshop and Symposium. At this workshop, the outcomes of 14,702 patients diagnosed with Hodgkin’s disease between the early 1960s and 1987 were pooled, allowing for an analysis of results that extended over approximately 20 years (Henry-Amar M, Aeppli DM, Anderson J, et al. Long term survival and study of causes of death. In: Somers R, Henry-Amar M, Meerwaldt JK, Carde P, eds. Treatment Strategy in Hodgkin’s Disease. London: John Libbey and Co; 1990: 381–418). This analysis included 9041 patients assessed as having "early-stage" Hodgkin’s disease; 1957 (22%) of these patients had died. An actuarial analysis of cumulative deaths by cause demonstrated that over the first decade of follow-up, most deaths were directly attributed to Hodgkin’s disease. However, by 13 years of follow-up, deaths attributed to other causes surpassed those due to progressive Hodgkin’s disease. Furthermore, the observed number of deaths attributed to other causes exceeded those expected in comparison with an age- and gender-matched control group. Specific "other" causes of death included an increased occurrence of cardiovascular events and second cancers. As new treatment strategies improve control of Hodgkin’s lymphoma and reduce the incidence of death from this cause, recent randomized controlled trials evaluating therapy in patients with limited-stage disease already demonstrate, with much shorter durations of follow-up, that causes other than progressive Hodgkin’s lymphoma or acute treatment-related toxicity will account for the majority of deaths. In a randomized trial comparing extended-field radiation therapy with combined-modality therapy, Sieber et al observed that with a median follow-up of 22 months, 17 deaths had been observed in 572 patients; 10 deaths (59%) were attributed to causes other than progressive Hodgkin’s lymphoma or acute treatment-related toxicity (Sieber M, Franklin J, Tesch H, et al. Two cycles ABVD plus extended field radiotherapy is superior to radiotherapy alone in early stage Hodgkin’s disease: results of the German Hodgkin’s Lymphoma Study Group (GHSG) Trial HD7 [abstract]. Blood. 2002;100:93a). In a randomized trial comparing a strategy that includes radiation therapy with chemotherapy alone, Meyer et al observed that with a median follow-up of 4.2 years, 15 deaths had been observed in 399 patients; 9 deaths (60%) were attributed to causes other than progressive Hodgkin’s lymphoma or acute treatment-related toxicity (Meyer RM, Gospodarowicz M, Connors J, et al. A randomized phase III comparison of single-modality ABVD with a strategy that includes radiation therapy in patients with early-stage Hodgkin’s disease: the HD-6 trial of the National Cancer Institute of Canada Clinical Trials Group (Eastern Cooperative Oncology Group Trial JHD06) [abstract]. Blood. 2003;102:26a). Thus, to further improve long-term survival, reduction in deaths from other causes will become the major focus of new interventions. 2 basic principles of clinical trial design require attention in order to reduce the risk of bias that might confound resulting conclusions (Sackett DL, Haynes RB, Guyatt GH, Tugwell P. Clinical Epidemiology: A Basic Science for Clinicians. Toronto: Little, Brown and Co; 1991). The first principle requires that when a study aim is to determine the clinical course of a disease or prognosis of specific patient groups, it is necessary to evaluate an inception cohort of patients with the specific disease who have been identified at a relatively uniform time point in the disease process. The second principle requires that when a study aim is to evaluate whether new interventions should replace an existing form of therapy, these interventions should be tested in randomized controlled trials. Particularly in evaluating new modalities of therapy, systematic reviews that include meta-analyses of randomized trials testing similar interventions can enhance an understanding of the consistency, precision and generalizability of trial results^ref. Randomized controlled trials and meta-analyses need to include evaluations of relevant outcome measures that would properly inform determinations of standard treatment policies. For most clinical problems, a hierarchy of relevant outcomes can be constructed (Meyer RM, Kouroukis CT. Understanding outcome measures. Evidence-based Oncol. 2001;2:172–176). This hierarchy includes specific domains such as survival, quality of life and health care economics. Often other outcomes that serve as proxy measures for these specific domains will be reported; these surrogate measures can include parameters of disease control or treatment-related toxicity that might predict for overall survival or quality of life. The use of surrogate outcomes to formulate standard treatment practices requires caution as the predictiv