Epidemiological evidence for the 'two-disease hypothesis' in Hodgkin's disease

Detection of Epstein-Barr virus and genotyping based on EBNA2 protein in Mexican patients with hodgkin lymphoma: a comparative study in children and adults

BACKGROUND

Epstein-Barr virus (EBV) is a member of the Herpesviridae family and is associated with Hodgkin lymphoma (HL). Isolates of EBV are classified according to sequence variation in the latency genes such as Epstein-Barr virus nuclear antigen (EBNA). EBNA2 contains the most divergent locus and is classified into type 1 and type 2 or EBNA2A and EBNA2B, respectively. We compared the frequency of EBV and the distribution of EBNA genotypes in Mexican children and adults with HL.

PATIENTS AND METHODS

Lymph node biopsy specimens from children and adults with HL were embedded in paraffin. EBV was identified by LMP1 amplification and Epstein-Barr-encoded RNA EBER by in situ hybridization (ISH) and genotyped as EBNA2A or EBNA2B using nested polymerase chain reaction (PCR) and specific primers for the detection of subtype.

RESULTS

Sixty-six samples were obtained from 3 hospitals-42 (63%) from children and 24 (37%) from adults with HL. Thirty-two of the 42 samples (76.1%) were positive for EBV in children and 16 of 24 (66.6%) samples were positive in adults (P = .41). In both children and adults, EBV was found more frequently in male patients. Thirty-four of 48 cases could be typed (70.8%). EBNA2A was found in 7/21 (33.3%) children and in 4/13 (30.8%) adults (P = 1.0), and EBNA2B was found in 10/21 (47.6%) children and in 9/13 (69.2%) adults (P = .22). A mix of subtypes was found in 4/21 (19%) children.

CONCLUSION

EBV was found frequently in both children and adults with HL. EBNA2B was the most frequent subtype, and a high frequency of mixed subtypes was found in children.

Level of education and the risk of lymphoma in the European prospective investigation into cancer and nutrition

INTRODUCTION

Lymphomas belong to the few cancer sites with increasing incidence over past decades, and only a few risk factors have been established. We explored the association between education and the incidence of lymphoma in the prospective EPIC study.

MATERIALS AND METHODS

Within 3,567,410 person-years of follow-up, 1,319 lymphoma cases [1,253 non-Hodgkin lymphomas (NHL) and 66 Hodgkin lymphomas (HL)] were identified. Cox proportional hazard regression was used to examine the association between highest educational level (primary school or less, technical/professional school, secondary school, university) and lymphoma risk.

RESULTS

Overall, no consistent associations between educational level and lymphoma risk were observed; however, associations were found for sub-groups of the cohort. We observed a higher risk of B-NHL (HR = 1.31, 95% CI = 1.02–1.68; n = 583) in women with the highest education level (university) but not in men. Concerning sub-classes of B-NHL, a positive association between education and risk of B cell chronic lymphatic leukaemia (BCLL) was observed only in women. In both genders, the risk of diffuse large B cell lymphoma (DLBCL) was significantly lower for subjects with university degree (HR = 0.46, 95% CI = 0.27–0.79) versus lowest educational level. No association was found for HL.

CONCLUSION

We could not confirm an overall consistent association of education and risk of HL or NHL in this large prospective study; although, education was positively related to the incidence of BCLL and B-NHL (in women) but inversely to incidence of DLBCL. Due to limited number of cases in sub-classes and the large number of comparisons, the possibility of chance findings can not be excluded.

Viruses and Hodgkin lymphoma: no evidence of polyomavirus genomes in tumor biopsies

The epidemiology of young adult Hodgkin lymphoma (HL) suggests that delayed exposure to a common childhood pathogen may be involved in disease pathogenesis. The Epstein-Barr virus (EBV) is associated with a proportion of cases but cases of young adult HL in westernized countries are less frequently EBV-associated than cases in other age groups and geographical locales. This study investigated the possibility that polyomaviruses might be involved in the etiology of HL by analysing a series of 35 cases of classical HL using both specific and degenerate PCR assays for polyomavirus genomes. No positive results were obtained, indicating that it is highly unlikely that this virus family is directly involved in the pathogenesis of HL.

Personal and family history of autoimmune diabetes mellitus and susceptibility to young-adult-onset Hodgkin lymphoma

Young-adult-onset (15-44 years of age) Hodgkin lymphoma (HL) is believed to arise as a consequence of late primary infection in susceptible individuals. The properties of this susceptibility remain little understood. We have previously reported an increased occurrence of HL in patients with rheumatoid arthritis and among their offspring, suggesting that susceptibility to autoimmunity might be of importance also in the pathogenesis of HL. To explore this hypothesis, we assessed the association of personal and family history of diabetes mellitus, with risk of subsequent HL in a population-based case-control study, including as cases all individuals diagnosed with HL above 15 years of age 1964-1999 (n = 6,873) in Sweden, and matched population controls (n = 12,565). First-degree relatives of cases and controls were identified through linkage with the Multi-generation Register. We identified discharges listing diabetes mellitus through linkage with the Inpatient Register (1964-2000). We used odds ratios (OR) as measures of relative risk. Cases with young-adult-onset HL were less likely to have a personal (OR =0.5, 95% CI 0.2-1.1) or family (OR =0.7, 95% CI 0.6-0.8) history of diabetes mellitus. In contrast, HL diagnosed at older ages was neither associated with a personal (OR =1.0) nor family (OR =1.0) history of diabetes mellitus. These findings suggests that characteristics of the immune system associated with conditions such as diabetes mellitus type I are of importance in the pathogenesis of young-adult-onset HL.

Family history of hematopoietic malignancy and risk of lymphoma

BACKGROUND

A family history of hematopoietic malignancy is associated with an increased risk of non-Hodgkin lymphoma (NHL) and Hodgkin lymphoma (HL), although the magnitude of the relative risk is unclear. We estimated the association between familial hematopoietic cancer and risk of lymphoma using validated, registry-based family data, and we also investigated whether associations between some environmental exposures and risk of lymphoma vary between individuals with and without such a family history.

METHODS

In a population-based case-control study of malignant lymphoma, 1506 case patients and 1229 control subjects were linked to the Swedish Multi-Generation Register and then to the Swedish Cancer Register to ascertain history of cancer in first-degree relatives of patients with malignant lymphoma. Multiple logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for associations with the risk of lymphoma.

RESULTS

A history of hematopoietic malignancy in any first-degree relative was associated with an increased risk of all NHL (OR = 1.8, 95% CI = 1.2 to 2.5), common B-cell NHL subtypes, and HL. Relative risks were generally stronger in association with sibling hematopoietic cancer (OR for all NHL = 3.2, 95% CI = 1.3 to 7.6) than with parental hematopoietic cancer (OR = 1.6, 95% CI = 1.1 to 2.3). A family history of NHL or chronic lymphocytic leukemia (CLL) was associated with an increased risk of several NHL subtypes and HL, whereas familial multiple myeloma was associated with a higher risk of follicular lymphoma. There was no statistically significant heterogeneity in NHL risk associations with environmental factors between individuals with and without familial hematopoietic malignancy.

CONCLUSIONS

The increased risk of NHL and HL among individuals with a family history of hematopoietic malignancy was approximately twofold for both lymphoma types. There was no evidence that etiologic associations varied between familial NHL and nonfamilial NHL.

Body Mass Index and Risk of Malignant Lymphoma in Scandinavian Men and Women

BACKGROUND

The incidence of non-Hodgkin lymphoma and prevalence of obesity are increasing globally. A suggested positive association between obesity and risk of non-Hodgkin lymphoma has prompted us to investigate the relationship between body mass index (BMI) and risk of malignant lymphoma subtypes in a population-based case-control study.

METHODS

Telephone interviews were conducted with 3055 case patients with non-Hodgkin lymphoma and 618 case patients with Hodgkin lymphoma diagnosed between October 1, 1999, and August 30, 2002, and 3187 population-based control subjects. The interviews assessed current height, normal adult weight, and other possible risk factors. Multivariable odds ratios (ORs) and corresponding 95% confidence intervals (CIs) for risk of lymphoma were estimated by unconditional logistic regression. All statistical tests were two-sided.

RESULTS

BMI was not associated with risk of overall non-Hodgkin lymphoma or of Hodgkin lymphoma (for example, comparing the highly obese group [BMI > or =35.0 kg/m2] with the normal-weight group [BMI = 18.5-24.9 kg/m2], OR for risk of non-Hodgkin lymphoma = 0.9, 95% CI = 0.6 to 1.3; P(trend) across all categories of BMI = .27). BMI was also not associated with risk of any non-Hodgkin lymphoma subtype evaluated, although there was some evidence of a positive association with risk of diffuse large B-cell lymphoma (for example, comparing the highly obese group with the normal-weight group, OR for diffuse large B-cell lymphoma = 1.5, 95% CI = 0.9 to 2.4; P(trend) =.05).

CONCLUSIONS

Excess weight does not appear to be associated with an increased risk of malignant lymphoma in general, or with a risk of most major lymphoma subtypes. Hence, the growing incidence of obesity is unlikely to be an important contributor to the increasing incidence of non-Hodgkin lymphoma worldwide.

Seasonal variation in the diagnosis of Hodgkin lymphoma in Sweden

Epidemiologic evidence suggests a seasonal pattern in the occurrence of Hodgkin lymphoma (HL), with an incidence peak around the month of March. This pattern may reflect seasonal variation in the prevalence of an infectious agent involved in HL development. Using Poisson regression, we examined monthly variation in HL diagnosis in Sweden between 1958 and 1998, based on data from the population-based Swedish Cancer Registry. Older adults (50 to 79 years) were marginally more likely to be diagnosed in February, but there was no monthly variation after stratifying by sex. Young adult males (15 to 49 years) presented more often in February, whereas young adult females presented less often in August and December. Among children (<15 years), boys were significantly more likely to have been diagnosed in March, whereas there was no seasonal incidence pattern among girls. The seasonal pattern in HL diagnosis among young adults and boys is consistent with an infectious origin, whereas the results among older adults neither support nor dispute the possibility of an infectious etiology in this age group.

Childhood Social Environment and Hodgkin's Lymphoma: New Findings from a Population-Based Case-Control Study

Background: Risk of Hodgkin's lymphoma in young adults has previously been associated with higher childhood socioeconomic status (SES) and other markers of delayed infection with common childhood pathogens, especially the Epstein-Barr virus. This study examines the current role of childhood social environment in the development of Hodgkin's lymphoma. Methods: A population-based case-control study of 565 Hodgkin's lymphoma cases and 679 controls was conducted in the Boston, MA metropolitan area and the state of Connecticut to investigate the viral etiology of Hodgkin's lymphoma. Results: A novel association was detected between attendance of nursery school or day care and reduced risk of Hodgkin's lymphoma among individuals ages 15 to 54 years. The odds ratio (95% confidence interval) for having attended preschool for at least 1 year was 0.64 (0.45-0.92). Risk of young-adult Hodgkin's lymphoma was also associated with family history of hematopoietic cancer, Jewish ethnicity, and cigarette smoking. Other indicators of childhood SES were not associated with young-adult Hodgkin's lymphoma. Among older adults ages 55 to 79 years, Hodgkin's lymphoma was associated with lower childhood SES but not with preschool attendance. Conclusions: Early exposure to other children at nursery school and day care seems to decrease the risk of Hodgkin's lymphoma in young adults, most likely by facilitating childhood exposure to common infections and promoting maturation of cellular immunity. This finding supports the delayed infection model of Hodgkin's lymphoma etiology in young adults while introducing a new major determinant of age at infection. Hodgkin's lymphoma seems to have a separate pathogenesis among older adults.

Number of Siblings and Risk of Hodgkin's Lymphoma

Background: Epidemiologic evidence indicates that risk of Hodgkin's lymphoma (HL) in young adults is associated with correlates of delayed exposure to infection during childhood. In contrast, HL among children and older adults may be associated with earlier childhood infection. This study examines the associations of HL risk with having older or younger siblings. Methods: We conducted a case-control study in Sweden comparing 2,140 HL patients identified from the Swedish Cancer Register with 10,024 controls identified from national population registers. The Swedish Multi-Generation Register was used to link individuals to their parents and siblings. Results: Among young adults ages 15 to 39 years, the odds ratios (OR) associated with having one, two, and three or more older siblings, compared with none, were 0.96 [95% confidence interval (CI), 0.82-1.13], 0.88 (95% CI, 0.72-1.09), and 0.72 (95% CI, 0.55-0.93), respectively (P value for trend = 0.01). In contrast, number of older siblings was not associated with HL risk among children or older adults. Number of younger or total siblings, mother's age at birth, and father's occupation were not associated with HL at any age. The decreased risk of young-adult HL did not vary appreciably by age difference or sex of older siblings. Conclusions: Risk of HL was lower among young adults with multiple older but not younger siblings. Having older siblings is associated with earlier exposure to common childhood pathogens. Pediatric and older-adult HL were not associated with number of siblings, suggesting a different pathogenesis of disease in these age groups.

Aspirin and the Risk of Hodgkin's Lymphoma in a Population-Based Case-Control Study

BACKGROUND

Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with decreased risk of several malignancies. NSAIDs may prevent cancer development by blocking the cyclooxygenase-catalyzed synthesis of proinflammatory prostaglandins. Aspirin may also protect against Hodgkin's lymphoma by inhibiting transcription factor nuclear factor kappaB (NF-kappaB), which is necessary for immune function and the survival of Hodgkin's lymphoma cells. We examined the association between regular analgesic use and the risk of Hodgkin's lymphoma.

METHODS

A population-based case-control study of 565 case patients with Hodgkin's lymphoma and 679 control subjects was conducted in the metropolitan area of Boston, Massachusetts, and in the state of Connecticut. Participants reported their average use of aspirin, non-aspirin NSAIDs, and acetaminophen over the previous 5 years. Regular analgesic use was defined as consumption of at least two tablets per week on average over the preceding 5 years; non-regular use was defined as consumption of fewer than two tablets per week.

RESULTS

The risk of Hodgkin's lymphoma associated with regular aspirin use was statistically significantly lower (odds ratio [OR] = 0.60, 95% confidence interval [CI] = 0.42 to 0.85) than that associated with non-regular aspirin use. The risk was not associated with use of other non-aspirin NSAIDs (OR = 0.97, 95% CI = 0.73 to 1.30). However, the risk associated with regular acetaminophen use was statistically significantly higher (OR = 1.72, 95% CI = 1.29 to 2.31) than that associated with non-regular use.

CONCLUSION

The inverse association between aspirin, but not other NSAIDs, and Hodgkin's lymphoma suggests that NF-kappaB signaling may play a key role in Hodgkin's lymphoma pathogenesis.

Viruses and Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is unusual among human malignancies in that the epidemiology suggests an infectious aetiology. The Epstein-Barr virus (EBV) is associated with a proportion of cases and this association is believed to be causal. In these cases the Hodgkin and Reed-Sternberg (HRS) cells express the EBV-encoded proteins LMP1 and LMP2, which can mimic CD40 and the B cell receptor, respectively, and therefore may play a critical role in facilitating the survival of HRS cells. EBV-associated and non-EBV-associated HL cases have different epidemiological features and recent data suggest that delayed exposure to EBV is a risk factor for the development of EBV-associated HL in young adults. We suggest that HL can be divided into four entities on the basis of EBV status and age at presentation, with three groups of EBV-associated cases and a single group of EBV-negative cases. The aetiology of the latter cases is obscure although involvement of an infectious agent(s) is suspected.

Viruses and Hodgkin disease: no evidence of novel herpesviruses in non-EBV-associated lesions

The Epstein-Barr virus (EBV) is associated with a proportion of cases of Hodgkin disease (HD) and this association is believed to be causal. Epidemiological studies suggest that an infectious agent is involved in the aetiology of young adult HD, however, cases in this age group are less likely to have EBV-associated disease than cases diagnosed in early childhood or older adult years. Molecular studies have failed to find a consistent association between HD and other candidate viruses, and the aetiology of non-EBV-associated cases remains obscure. We looked for evidence of herpesvirus infection in samples of non-EBV-associated HD using a highly sensitive, degenerate PCR assay. Despite exhaustive sequence analysis of PCR products, no novel herpesviruses were identified. These results suggest that it is extremely unlikely that a novel herpesvirus is involved in the pathogenesis of non-EBV-associated HD.

Variation in the frequency of Epstein-Barr virus-associated Hodgkin's disease with age

A number of studies in developed countries have reported variation in the frequency of Epstein-Barr virus (EBV)-associated Hodgkin's disease (HD) with age. A 'three disease' model for HD that incorporates the EBV association, histological subtype of HD and age has recently been proposed. In this model, Hodgkin's disease of childhood and older adults is commonly EBV-associated and of mixed cellularity type, whereas young adult HD is generally not EBV-associated and is usually characterised by nodular sclerosis disease. A case series of HD diagnosed in the West Midlands between 1981 and 1997, inclusive, was used to investigate the applicability of the 'three disease' model. In situ hybridisation for the EBV early RNAs (EBERs) was used to determine the presence of EBV in the malignant Hodgkin/Reed-Sternberg cells. In contrast to the 'three disease' model, nodular sclerosis was the predominant subtype in each of the age groups within the case series. In addition, overall there was little variation in EBV-positive rates across the age ranges examined. However, when females were analysed separately, older women (45+ years) were significantly more likely to have EBV-positive disease than their younger counterparts (<45 years). In summary our results do not generally support the 'three disease' model.

Space-time clustering of Hodgkin's Disease in parts of the UK, 1984-1993

The object of this study was to examine cases of Hodgkin's Disease (HD) for evidence of space-time clustering of onsets by age group, sex and disease subtype. Data comprised 2024 cases of HD aged 0-79 years arising throughout the period 1984 to 1993 in the areas covered by a specialist population based register of leukaemias and lymphomas. Knox space-time analysis was used separately for 3 different age groups: childhood (0-14 years), young adult (15-34 years) and older adults (35-79 years); for adult cases separate analysis was carried out by sex and for the nodular and non-nodular sclerosing subtypes. Results showed that space-time clustering of onsets was limited to the nodular sclerosing cases. It was more prominent in young adult nodular sclerosing cases aged 15-34 years (particularly females) diagnosed in the period 1984-88, than in those diagnosed in 1989-93. We conclude that clustering may provide further evidence that an infectious process is involved in the aetiology of young adult nodular sclerosing cases of HD.

Further investigation of the role of HLA-DPB1 in adult Hodgkin's disease (HD) suggests an influence on susceptibility to different HD subtypes

It has been suggested in a number of studies that susceptibility to adult Hodgkin's disease (HD) is influenced by the HLA class II region, and specifically by alleles at the HLA-DPB1 locus. Since HD is diagnostically complex, it is not clear whether different HLA-DPB1 alleles confer susceptibility to different HD subtypes. To clarify this we have extended a previous study to type DPB1 alleles in 147 adult HD patients from a single centre. We have analysed patients with nodular sclerosing (NS), mixed cellularity (MC) or lymphocyte predominant (LP) HD, and gender in relation to HLA-DPB1 type, in comparison with 183 adult controls. The results confirmed previously reported associations of DPB1*0301 with HD susceptibility (relative risk (RR) = 1.42; 95% confidence interval (CI) 0.86-2.36) and DPB1*0201 with resistance to HD (RR = 0.49; CI 0.27-0.90). However, analysis by HD subtype and gender showed that *0301-associated susceptibility was confined to females with HD (RR = 2.46; CI 1.02-5.92), and *0201-associated resistance to females with NS-HD (RR = 0.28; CI 0.10-0.79). Susceptibility to NS-HD was also associated in females with *1001 (RR = 11.73; CI 1.32-104.36), and resistance with *1101 (RR = 0.08; CI 0.01-0.65). In contrast, susceptibility to LP-HD was associated in males with *2001 (RR = 32.14; CI 3.17-326.17), and to MC-HD with *3401 (RR = 16.78; CI 2.84-99.17). Comparison of DPB1-encoded polymorphic amino-acid frequencies in patients and controls showed that susceptibility to MC-HD was associated with Leucine at position 35 of DPB1 (RR = 8.85; CI 3.04-25.77), Alanine-55 (RR = 15.17; CI 2.00-115.20) and Valine-84 (RR = 15.94; CI 3.55-71.49). In contrast, Glutamic acid 69 was significantly associated with resistance to MC-HD (RR = 0.14; CI 0.03-0.60). Certain DPB1 alleles and individual DPbeta1 polymorphic amino acid residues may thus affect susceptibility and resistance to specific HD subtypes. This may be through their influence on the binding of peptides derived from an HD-associated infectious agent, and the consequent effect on immune responses to the agent.

Incidence and time trends in Hodgkin's disease: from parts of the United Kingdom (1984-1993)

Over 3,000 cases of Hodgkin's Disease diagnosed between 1984-93 were used to examine incidence and time trends. These data are part of the Leukaemia Research Fund's specialist Data Collection Study, which is the only large, population-based data set of its type in Europe. The age specific incidence curves showed different patterns for nodular sclerosis contrasted with all other subtypes combined (non-nodular sclerosis). For nodular sclerosis, there was a female excess for young adults, while for non-nodular sclerosis a gradual rise in incidence with age in both sexes was observed. Incidence varied over time, showing a complex pattern with a decreasing trend in males in all Rye-subtypes and no significant change among females diagnosed with nodular sclerosis. These complex patterns of change are different from those seen in other countries. It is concluded that the results provide clear evidence of the heterogeneity of Hodgkin's disease between the sexes and between subtypes, which should be taken into account in future studies.

What causes Hodgkin's disease in children?

Hodgkin's disease is one of the commonest cancers of older children and adolescents, but little is known about its aetiology. Recent data, particularly in descriptive epidemiology and virology, tend to confirm the 'two-disease' hypothesis. Mixed cellularity Hodgkin's disease is more common, especially at younger ages, in poorer socioeconomic environments, whereas nodular sclerosing Hodgkin's disease has a higher incidence in more affluent societies. Approximately three-quarters of childhood Hodgkin's disease, and a higher proportion of the mixed cellularity subtype, may be a rare response to Epstein-Barr virus infection, together with an unidentified cofactor related to the degree of affluence of the population. Other infectious agents may be implicated in some cases. The already low incidence, especially of nodular sclerosis, among populations of East Asian ethnic origin and the high incidence, especially of mixed cellularity, among some populations of South Asian origin are apparently independent of socioeconomic status. This ethnic variation in risk suggests that genetic predisposition also plays a role. Detailed HLA studies may help to elucidate the complex variations between populations in the risk of Hodgkin's disease and its principal subtypes.

Epstein-Barr virus in pediatric Hodgkin disease: age and histiotype are more predictive than geographic region

Epidemiologic studies have implicated Epstein-Barr virus (EBV) in the great majority (80%-100%) of Hodgkin disease (HD) cases in South American countries, versus only 30%-40% in the United States and other industrialized countries. Other EBV-related malignancies are known to be geographically localized, including nasopharyngeal carcinoma in south China and Burkitt lymphoma in equatorial Africa. Some studies, however, have suggested that age and histiotype, rather than geographic region, are the major determinants of the association between EBV and HD. To further characterize this relationship in children, we matched 26 cases of pediatric Hodgkin disease from south Brazil and 26 cases from the U.S.-forhistiotype and age. The Brazilian children (22 males, 4 females) had a median age of 9 years, while the median age of the U.S. group (11 males, 15 females) was 7.5 years. Formalin-fixed, paraffin-embedded biopsy material was examined for EBV early RNA1 (EBER1) expression by in situ hybridization. This antigen was detected solely in Reed-Sternberg cells or their variants in positive samples. The same proportion of cases was positive (15/26 or 58%) in both groups of children. After adjustment for histiotype and age, the association between EBV and HD remained independent of geographic location, but was more frequent in children aged < or = 10 years at diagnosis. These findings support the multiple-etiology hypothesis for Hodgkin disease.

Infectious mononucleosis and Hodgkin's disease--a similar seasonality

The presentation of Hodgkin's disease and acute infectious mononucleosis (glandular fever) due to Epstein-Barr virus, have similar seasonal features with the peak incidence around March. The extent of seasonal variation is also similar. Seasonality of Hodgkin's disease is most obvious and also significant in adult age groups below the age of 40. Amongst those over 40 years, seasonality was no longer present in the 40-59 but returned over age 60. Seasonal similarity does not prove a relationship. However two speculations are made on possible mechanisms. Firstly glandular fever may accelerate presentation in young adults, destined to present with HD. Secondly the Epstein-Barr virus may have an inherent seasonal behaviour whether causing acute infectious mononucleosis or when latent and playing a role in the aetiology of Hodgkin's disease.

Epidemiology of EBV and Hodgkin's lymphoma

The incidence of Hodgkin's disease shows marked heterogeneity with respect to age, gender, race, geographical locale, social class and histological subtype. The Epstein-Barr virus (EBV) is associated with a proportion of cases, approximately 40% in developed countries, and there is a body of evidence which suggests that mixed cellularity Hodgkin's disease is more likely to be EBV-associated than nodular sclerosis Hodgkin's disease. This study investigates the relationship between EBV and both age and histological subtype. We confirm the above subtype distribution and that childhood and older adult cases are more likely to be EBV-associated than young adult cases. Young adult nodular sclerosis cases are rarely EBV-associated providing further evidence that this is a separate disease entity. The results of this study support the multiple aetiology hypothesis which suggests that Hodgkin's disease in different age groups has different aetiologies. The epidemiology of Hodgkin's disease and studies investigating the distribution of EBV-associated cases are reviewed.

Case clustering, Epstein-Barr virus Reed-Sternberg cell status and herpes virus serology in Hodgkin's disease: results of a case-control study

The Leukaemia Research Fund Data Collection Study (DCS) is a specialist registry of leukaemias and lymphomas. The present study involves 494 cases of Hodgkin's disease (HD) registered with the DCS between 1985 and 1989. This entire data set has been tested for localised spatial clustering using an established nearest neighbour method with 18% of all cases in young people classified as clustered (P < 0.05). No clustering was found in older cases. Subsamples were selected from the registered cases for a pilot study in which case clustering, herpes virus antibody titres and Epstein-Barr virus (EBV) presence within the Reed-Sternberg (RS) cells (EBV-RS status) were investigated together. Firstly, a case-control study of HD in young people or nodular sclerosing (NS) subtype (39 HD cases and 26 healthy controls) found significant elevation of antibody titres to EBV-viral capsid antigen (VCA), EBV-early antigen (EA) and human herpes virus 6 (HHV-6) in HD cases compared with controls. EBV viral genome was present in 5 cases and 4 of these were in clusters of HD in young people. Elevation of antibody titres to the EBV antigens was not associated with case clustering or EBV-RS status. Antibody titres to HHV-6 differed significantly between EBV-RS+ and EBV-RS- cases (P = 0.04). Geometric mean titres for HHV-6 for EBV-RS+ and EBV-RS- cases were 11.5 and 73.7, respectively, with the former lower than the control value of 20.5. Secondly, a cluster study included all other cases (n = 14) in clusters containing known EBV-RS+ cases. 3 further cases were EBV-RS+ positive but no cluster consisted entirely of positive cases. Overall, 5/16 clustered, 2/12 peripheral and 1/25 random cases in these studies were EBV-RS+ (P = 0.017). The interpretation of these results in terms of shared aetiological exposures of cases within clusters and the roles of EBV and HHV-6 is discussed, and hypotheses for testing in future studies proposed.

Evidence for a seasonal variation in the presentation of Hodgkins disease

An analysis by month of diagnosis was made of 1359 cases of Hodgkins disease (HD) on the Scotland and Newcastle Lymphoma Group (SNLG) registry 1979-1992 to look for evidence of seasonality. A March peak was evident when all cases were analysed (p < 0.01). The histological subtypes nodular sclerosing (NS) and mixed cellularity (MC) showed a similar pattern (p < 0.05) while lymphocyte depleted (LD) and lymphocyte predominant (LP) had no demonstrable seasonal variation. In a breakdown by age and sex there was evidence of seasonality in both sexes but only under the age of 40. This provides further evidence for the heterogeneity of HD and supports the hypothesis that different factors are involved in the aetiology of this condition in younger compared to older patients.

Hodgkin's disease: the protective effect of childbearing

Register and census data for complete cohorts of Norwegian men and women born between 1935 and 1974 were used to examine the relationship between reproductive factors and the incidence of Hodgkin's disease (HD). Among 1.3 million men and 1.3 million women under observation, 695 male and 441 female cases of HD were diagnosed during the period of follow-up. Our hazard model estimates showed that women, at a given age and in a given birth cohort, have an HD incidence inversely related to current parity. A clear relationship was found only for the nodular sclerosis subtype. In men, the risk of HD development was higher than that in childless women, and there was no parity effect. The lower HD incidence among high-parity women could not be ascribed to their lower social status. Presumably, there is a still unidentified protective factor associated with the biology of childbearing, the effect of which possibly wears off with increasing length of time since childbirth. In addition, there are indications of a net effect of age at entry into motherhood, which may explain part of the estimated parity effect.

Viral involvement in Hodgkin's disease

The etiology of Hodgkin's disease (HD) is unknown, but a growing body of evidence suggests that the Epstein-Barr virus (EBV) plays a role in a proportion of cases. Clonal EBV genomes have been detected in affected tissues, and EBV has been localized to Reed-Sternberg (RS) cells, the putative malignant cells in HD. EBV latent genes, including the EBER RNAs and the latent membrane protein, LMP-1, are expressed by RS cells. These data suggest that EBV is playing a role in the pathogenesis of HD; however, it is clearly not involved in all cases. Using in situ hybridization, we can detect EBV within the RS cells in approximately 40% of cases. Epidemiological data suggest that HD is a heterogeneous condition and the distribution of EBV-associated cases is not random. Studies from several groups indicate that mixed cellularity cases are more likely to be EBV-associated than nodular sclerosis cases. Our data further suggest that the majority of pediatric and older cases of HD are EBV-associated, whereas the RS cells in young adult cases only rarely harbor EBV. We therefore speculate that another virus is responsible for the young adult peak in incidence which is seen in developed countries.

Hodgkin's disease

The epidemiological features of Hodgkin's disease (HD) suggest that it is a heterogeneous condition which may have different aetiologies in different age groups. The risk factors for the development of HD in young adults suggest that delayed exposure to a common infectious agent may be involved in this age group. Seroepidemiological studies have shown that HD patients have elevated antibody titres to Epstein-Barr virus (EBV) and the elevated titres have been shown to precede the diagnosis of HD. Recent molecular studies provide support for the idea that EBV is involved in the pathogenesis of HD. EBV genomes are consistently found in a proportion of tumour biopsies, the EBV-infected cells are clonal and the EBV genomes have been localized to Reed-Sternberg cells. Furthermore, EBV latent gene products are expressed by the Reed-Sternberg cells. The majority of HD samples from patients aged greater than 50 years and less than 15 years are EBV positive, whereas the minority (less than 15%) of samples from young adults contain detectable EBV DNA. The results suggest that EBV plays a role in HD in children and older adults but that other agents, possibly other viruses, are involved in young adults.