Hodgkin's disease, work, and the environment. A review

Current insight on trends, causes, and mechanisms of Hodgkin's lymphoma

Hodgkin's lymphoma (HL) has a unique and distinct history, epidemiology, treatment, and biology. A viral agent or infectious agent has long been considered as the etiologic agent and Epstein-Barr virus is the main candidate for the infectious agent causing HL; however, Epstein-Barr virus genome is found within the tumor in only about 20% to 40% of HL cases with a prior diagnosis of infectious mononucleosis. Recently, autoimmune and related conditions have drawn attention to a potential role for immune-related and inflammatory conditions in the etiology and pathogenesis of the malignancy. Evidence from multiply-affected families, a twin study, a case-control study, and population-based registry studies implicate genetic factors. Data from Eastern Asia and among Chinese immigrants in North America indicate increasing incidence trends for HL being associated with westernization. These results emphasize an interaction between environmental and genetic risk factors in HL.

Mortality from lymphohematopoietic malignancies among workers in formaldehyde industries: the National Cancer Institute Cohort

BACKGROUND

Formaldehyde exposure is associated with leukemia in some epidemiological studies. In the National Cancer Institute's formaldehyde cohort, previously followed through December 31, 1979, and updated through December 31, 1994, formaldehyde exposure was associated with an increased risk for leukemia, particularly myeloid leukemia, that increased with peak and average intensity of exposure.

METHODS

We extended follow-up through December 31, 2004 (median follow-up = 42 years), for 25 619 workers employed at one of 10 formaldehyde-using or formaldehyde-producing plants before 1966. We used Poisson regression to calculate relative risk (RR) estimates and 95% confidence intervals (CIs) to examine associations between quantitative formaldehyde exposure estimates (peak exposure, average intensity and cumulative exposure) and death from lymphohematopoietic malignancies. All statistical tests were two-sided and considered to be significant at P = .05.

RESULTS

When follow-up ended in 2004, there were statistically significant increased risks for the highest vs lowest peak formaldehyde exposure category (> or =4 parts per million [ppm] vs >0 to <2.0 ppm) and all lymphohematopoietic malignancies (RR = 1.37; 95% CI = 1.03 to 1.81, P trend = .02) and Hodgkin lymphoma (RR = 3.96; 95% CI = 1.31 to 12.02, P trend = .01). Statistically nonsignificant associations were observed for multiple myeloma (RR = 2.04; 95% CI = 1.01 to 4.12, P trend > .50), all leukemia (RR = 1.42; 95% CI = 0.92 to 2.18, P trend = .12), and myeloid leukemia (RR = 1.78; 95% CI = 0.87 to 3.64, P trend = .13). There was little evidence of association for any lymphohematopoietic malignancy with average intensity or cumulative exposure at the end of follow-up in 2004. However, disease associations varied over time. For peak exposure, the highest formaldehyde-related risks for myeloid leukemia occurred before 1980, but trend tests attained statistical significance in 1990 only. After the mid-1990s, the formaldehyde-related risk of myeloid leukemia declined.

CONCLUSIONS

Evaluation of risks over time suggests a possible link between formaldehyde exposure and lymphohematopoietic malignancies, particularly myeloid leukemia but also perhaps Hodgkin lymphoma and multiple myeloma. Observed patterns could be due to chance but are also consistent with a causal association within the relatively short induction-incubation periods characteristic of leukemogenesis. Further epidemiological study and exploration of potential molecular mechanisms are warranted.

New aspects in descriptive, etiologic, and molecular epidemiology of Hodgkin's lymphoma

Epstein-Barr virus (EBV) has remained the main candidate suggested as the infection causing Hodgkin's lymphoma for several years. However, EBV genome has been found only within the tumor in about 20%-40% of Hodgkin's lymphoma cases with a prior diagnosis of infectious mononucleosis. Recently, autoimmune and related conditions have drawn attention to a potential role for immune-related and inflammatory conditions in the etiology and pathogenesis of the malignancy. Evidence from multiple affected families from case series, a twin study, a case-control study, and population-based registry studies implicate a role for genetic factors. Simultaneously, data from Eastern Asia and among Chinese immigrants in North America indicate increasing incidence trends for Hodgkin's lymphoma being associated with westernization. These results emphasize an interaction between environmental and genetic risk factors in Hodgkin's lymphoma.

Hodgkin lymphoma, multiple myeloma, soft tissue sarcomas, insect repellents, and phenoxyherbicides

OBJECTIVE

The objective of this study was to determine if there is an additional risk of developing Hodgkin lymphoma, multiple myeloma, or soft tissue sarcoma as a consequence of exposure to a combination of phenoxyherbicides, rubber gloves, DEET (N, N-diethyl-m-toluamide), and sunlight compared with each of the individual chemicals.

METHODS

This was a population-based study of men with specific cancers and age, province-matched control subjects.

RESULTS

No additional risk from these combinations of exposures of developing these three types of tumor was found in contrast to non-Hodgkin lymphoma.

CONCLUSIONS

The mechanisms by which phenoxyherbicides contribute to the risk of multiple myeloma and non-Hodgkin lymphoma may be different.

Cancer mortality in workers exposed to organochlorine compounds in the pulp and paper industry: an international collaborative study

The objective of this study was to evaluate cancer mortality in pulp and paper industry workers exposed to chlorinated organic compounds. We assembled a multinational cohort of workers employed between 1920 and 1996 in 11 countries. Exposure to both volatile and nonvolatile organochlorine compounds was estimated at the department level using an exposure matrix. We conducted a standardized mortality ratio (SMR) analysis based on age and calendar-period-specific national mortality rates and a Poisson regression analysis. The study population consisted of 60,468 workers. Workers exposed to volatile organochlorines experienced a deficit of all-cause [SMR = 0.91; 95% confidence interval (CI), 0.89-0.93] and all-cancer (SMR = 0.93; 95% CI, 0.89-0.97) mortality, with no evidence of increased risks for any cancer of a priori interest. There was a weak, but statistically significant, trend of increasing risk of all-cancer mortality with increasing weighted cumulative exposure. A similar deficit in all-cause (SMR = 0.94; 95% CI, 0.91-0.96) and all-cancer (SMR = 0.94; 95% CI, 0.89-1.00) mortality was observed in those exposed to nonvolatile organochlorines. No excess risk was observed in cancers of a priori interest, although mortality from Hodgkin disease was elevated (SMR = 1.76; 95% CI, 1.02-2.82) . In this study we found little evidence that exposure to organochlorines at the levels experienced in the pulp and paper industry is associated with an increased risk of cancer, apart from a weak but significant association between all-cancer mortality and weighted cumulative volatile organochlorine exposure.

A cohort mortality study of leather tanners in Tuscany, Italy

BACKGROUND

Work in leather tanning may involve exposure to a wide range of chemicals. Some of these are carcinogens or suspected carcinogens. Increased risk for a number of cancers have been reported, although there are considerable inconsistencies between studies. The present study investigates the mortality of leather tanners in Tuscany, Italy.

METHODS

Tanneries were selected from the 1996 Valdarno Inferiore Tanneries Census and were in operation since December 31, 1970. Employees were followed until December 31, 1998 through company records, and the National and Regional Death Index. Demographic and work history data were abstracted from company payrolls. Regional mortality rates were used to calculate Standardized Mortality Ratio (SMR). Analyses were completed for the overall cohort (men and women) and for men who ever worked as of finisher, chrome tanners, and vegetable tanner (only men).

RESULTS

The cohort consisted of 4,874 workers (4,150 males and 724 females) employed in 92 tanneries active in 1996 and operating on December 31, 1970. Ascertainment of vital status and cause of death were completed for all individuals by the end of follow-up, December 31, 1998. Males showed increases for cancer of the endocrine glands (SMR 5.67, 4 observed (obs), 90% Confidence Intervals (CI) 195-1,308), blood diseases (SMR 3.29, 4 obs, 90% CI 112-753), mental disorders (SMR 1.95, 6 obs, 90% CI 85-385), violence and accidents (SMR 1.30, 54 obs, 90% CI 102-163). Mortality from myeloid leukemia was increased in males (SMR 2.08, 5 obs, 90% CI 82-437) and in females (SMR 5.99, 2 obs, 90% CI 106-1,887). One death from nasal cancer was observed versus 0.2 expected. Mortality from lung cancer was increased among finishers (SMR 1.45, 19 obs, 90% CI 95-212), an increase was observed also for bladder cancer (SMR 1.25, 2 obs, 90% CI 22-393) and pancreatic cancer (SMR 1.20, 2 obs, 90% CI 21-379).

CONCLUSIONS

The study confirms previous observations among tanners of increased mortality from lung, bladder, and pancreatic cancer. Noteworthy are the increased mortality from myeloid leukemia together with the new findings of an increased mortality from endocrine glands tumors, blood diseases, and psychiatric disorders which should be considered with caution because of the small number of cases and the novelty of the observation.

Occupation and malignant lymphoma: a population based case control study in Germany

AIMS

To identify occupations suspected to be associated with malignant lymphoma and to generate new hypotheses about occupational risks in a multicentre, population based case control study.

METHODS

Male and female patients with malignant lymphoma (n = 710) aged 18-80 years of age were prospectively recruited in six study regions in Germany. For each newly recruited lymphoma case, a sex, region, and age matched control was drawn from the population registers. Odds ratios and 95% confidence intervals for major occupations and industries were calculated using conditional logistic regression analysis, adjusted for smoking (in pack-years) and alcohol consumption. Patients with specific lymphoma subentities were additionally compared with the entire control group using unconditional logistic regression analysis.

RESULTS

The following economic/industrial sectors were positively associated with lymphoma: food products, beverages, tobacco; paper products, publishing and printing; and metals. Chemicals; real estate, renting, and business activities were negatively associated with lymphoma diagnosis. The authors observed an increased overall lymphoma risk among architects; maids; farmers; glass formers; and construction workers. Shoemaking and leather goods making was negatively associated with the lymphoma diagnosis (although based on small numbers). In the occupational group analysis of lymphoma subentities, Hodgkin's lymphoma was significantly associated only with rubber and plastic products making; diffuse large B cell lymphoma risk was considerably increased among metal processors; follicular lymphoma showed highly significant risk increases for several occupational groups (medical, dental, and veterinary workers; sales workers; machinery fitters; and electrical fitters); and multiple myeloma showed a particularly pronounced risk increase for farmers as well as for agriculture and animal husbandry workers.

CONCLUSIONS

The results partly confirm previously defined occupational risks. Occupational risk factors for follicular lymphomas might differ from the overall risk factors for malignant lymphoma.

Occupational exposures and haematological malignancies: overview on human recent data

OBJECTIVE

Occupational causes of haematological malignancies are relatively uncommon, under-studied and under-identified. They are also often unrecognized by clinicians. This review summarizes the principal epidemiologic studies on this topic.

METHODS

We analyzed the recent relevant human data found in the Medline, the Pascal and the BDSP databases.

RESULTS

Benzene and ionizing radiation are the only agents conclusively demonstrated to be carcinogenic to the haematopoietic system. In particular, both exposures are strongly associated with acute myeloid leukaemia. Low doses of both may also be related to myeloid malignancies. Infectious agents and pesticides are also thought to induce lymphoproliferative cancers. Some studies show an association between haematological malignancies and low-frequency electromagnetic fields and organic solvents. All of these suspected occupational causes must be confirmed by further studies.

CONCLUSIONS

Better knowledge and understanding of occupational causes of haematological malignancies are necessary to improve their prevention and compensation.

Epidemiology of Hodgkin's disease and non-Hodgkin's lymphoma

This review considers in detail the descriptive and aetiological epidemiology of Hodgkin's disease and non-Hodgkin's lymphoma (NHL), with attention to histological subcategories when the literature allows. The aetiology of Hodgkin's disease remains only partially understood. There is evidence that Epstein-Barr virus (EBV) may be involved in the causation of some cases, and clinical immune deficiency is a risk factor for a few, but the evidence is not entirely consistent and other factors may also be important in causing the EBV-associated cases of Hodgkin's disease. The cause of EBV-unassociated cases remains obscure. For NHL, although it has been shown that some cases are related to immune deficiency and chronic antigenic stimulation, and especially to EBV in the context of immune deficiency, the causation of the majority of cases remains unknown. The increasing incidence of NHL, other than that related to AIDS, is also essentially unexplained. Epidemiological investigation of the aetiology of NHL and Hodgkin's disease is making steady progress, however, and there remain leads to be followed that may result in a better understanding and hence prevention.

Epidemiology of lymphomas

Non-Hodgkin lymphoma (NHL) is the fifth most common cancer in the US, with about 55,000 new cases estimated for the year 2000. According to the new Surveillance, Epidemiology, and End Results (SEER) data from 1973 to 1997, the age-adjusted incidence rates rose by about 80%, with an annual percentage increase of nearly 3%, which is faster than for the majority of cancers. The increasing incidence of NHL is largely unexplained. AIDS-related NHL accounts for some but not all of the increase. The American Cancer Society predicts about 7,400 new cases of Hodgkin Disease (HD) in the year 2000 in the US. The incidence of HD is consistently lower than that of NHL, and has decreased about 16% since the 1970s. Only a small portion of the decrease in HD incidence can be explained by misdiagnosis of HD as NHL. Further research is needed on the cofactors that predispose AIDS cases to lymphoma, as well as other possible causes of NHL such as immunosuppression, genetics, viruses, medical conditions, pesticides, solvents, hair dyes, and diet. Further evaluation of the role of viruses, occupational exposures, and genetics in the etiology of HD should prove valuable.