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Keywords:

  • cohort study;
  • nested case-control study;
  • insecticides;
  • herbicides;
  • non-Hodgkin's lymphomas;
  • Hodgkin's disease;
  • chronic lyrnphocytic leukemia

Abstract

BACKGROUND

The Tecumseh Community Health Study (TCHS), initiated in 1959 at the University of Michigan School of Public Health, has provided a resource for long term prospective studies of the incidence of cancer in the setting of a midwestern rural farming community.

METHODS

A survey of total and site specific cancer incidence among 7016 male and female adult residents from 1959-1987 was conducted, and the observed number compared with the expected number, based on the age-sex-race-calendar period-and site-specific cancer incidence rates reported by the Connecticut tumor registry. Based on the results of this survey, a hypothesis was advanced concerning the potential risks of exposures to insecticides and herbicides. This was pursued by analyzing for each county in Michigan the comparative annual number of acres and percentage of acreage treated with agricultural chemicals in 1978 and for the period 1982- 1987. Finally, because of the availability of information on lifestyle risk factors that had been collected in the 1960s on all participants, a nested case-control study was implemented.

RESULTS

The standardized incidence ratio (SIR), based on the observed number divided by the expected number of invasive cancer cases (all sites combined [excluding nonmelanoma skin cancer]), was not significant in females (SIR, 0.95; 95% confidence interval [CI], 0.86-1.05) nor males (SIR, 0.91; 95% CI, 0.81-1.01). A significant increase was demonstrated for males and females combined in the incidence of lymphopoietic neoplasms, namely non-Hodgkin's lymphoma, Hodgkin's disease, and chronic lymphocytic leukemia; the combined SIR was 1.40 (95% CI, 1.03-1.86; P = 0.03). In the Department of Commerce surveys of counties in Michigan, the Tecumseh area (Lenawee County) was ranked highest with respect to the average annual number of acres (240,000 or more) and the percent of acreage (40%) sprayed with herbicides and insecticides. A comparison of temporal trends for cancer incidence since 1973 was reviewed for the Wayne-Oakland-Macomb tricounty area, in which the survey estimated that less than 80,000 acres per year, or less than 8% of acreage, were treated with pesticides. The comparison of the Tecumseh cohort, for all sites combined, was not significantly different from expectation in females (SIR, 1.01; 95% CI, 0.89-1.14), and was decreased by more than 10% in males (SIR, 0.88; 95% CI, 0.77-1.00). However, the SIR for non-Hodgkin's lymphoma in females was significantly elevated (SIR, 1.92; 95% CI, 1.07-3.11, P = 0.02); the trend for increased risks of lymphomas and leukemias was also evident in males. In the nested case-control study, based on risk factor information documented prior to diagnosis, the relative risk of a family history of lymphoma, leukemia, or multiple myeloma was significantly increased among patients with lymphoproliferative neoplasms (odds ratio, 3.81; 95% C1, 1.49-9.79; P = 0.005).

CONCLUSIONS

This prospective epidemiologic study conducted in a rural farming community in Michigan has found significant increases in the incidence dence of lymphoproliferative cancers. A plausible hypothesis, consistent with the preliminary findings, is that the reported cancer pattern is an expression of risk resulting from sustained environmental exposures to agricultural chemicals, perhaps in conjunction with familial or genetic factors. Cancer 1996; 72763-70. © 1996 American Cancer Society.