Assessment of cancer clusters using limited cohort data with spreadsheets: application to a leukemia cluster among rubber workers

Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industries. Part XXX: Causal relationship between chronic myelogenous leukemia and benzene-containing solvents

Benzene and benzene-containing products and solvents have long been associated with bone marrow toxicity. Both animal studies and human epidemiological studies have shown statistically significant increases of leukemia and other lymphohematopoietic cancers in workers exposed to benzene. The most common leukemia that has been associated with benzene exposure, also called benzene poisoning, is acute myelocytic leukemia (AML). A review of the epidemiological literature on workers exposed to benzene or benzene-containing solvents and products shows, without question, that this exposure is significantly related to other types of leukemia and lymphoma. In this article, we review the literature on the relationship between benzene exposure and chronic myelogenous leukemia (CML) and find that benzene and benzene-containing products are significantly related to morbidity and mortality from CML.

Occupation, hobbies, and acute leukemia in adults

Occupational and industrial exposures have been implicated in the etiology of leukemia, yet uncertainty remains regarding potential high risk occupations. We examined the associations between self-reported occupations and hobbies and acute leukemia risk using data from 811 cases and 637 controls participating in a case-control study in the U.S. and Canada. We found that several occupations may increase the risk of acute leukemia, particularly occupations related to petroleum products, rubber, nuclear energy, munitions, plastics, and electronics manufacturing. Differences were noted according to histological type. Other occupations and hobbies were not clearly associated with risk.

Leukemia mortality and occupational exposure to rubber: a nested case-control study

OBJECTIVE

The excess risk of leukemia in rubber industry was considered to be real and attributed to the exposure to solvents, particularly benzene.

METHODS

Following a nested case-control study, we used the data of 7 leukemia deaths in 1973-1997 and 28 controls matched for sex and age from the same cohort of a rubber plant. Leukemia risks due to exposure to rubber were assessed, unadjusted and adjusted for non-occupational factors by conditional logistic regression.

RESULTS

OR for leukemia was found to be 7.81 (95% CI = 0.77-78) in grouped analysis for one or more years of work in the inner tire tube department. The models for continuous exposure variables indicated that working for one year in the inner tire tube department was associated with a 10 percent increment in the OR (95% CI = 1.00-1.24; score test for linear trend: chi 1(2) = 6.27, P = 0.012). The confounding effects studied could not be ruled out for the excess risks. No excess risk was found in the remaining four departments.

CONCLUSIONS

Because of widespread exposure to various carcinogens in the process of making inner tire tubes, removal of a single agent (benzene) may not eliminate the risk of leukemia in the entire industry.