CANCER INCIDENCE IN A GROUP OF WORKERS POTENTIALLY EXPOSED TO ETHYLENE-OXIDE

Background. Cytogenetic changes associated with ethylene oxide (ETO) e xposure at a worksite prompted a study of cancer incidence in that coh ort. Method. Cancer incidence through 31 December 1987 was ascertained in a cohort of 1132 individuals employed at the worksite at any time from 1 July 1974 through 30 September 1980, the period of potential ex posure to ETO at the plant. The number of observed cancers was compare d with that expected based on age- and sex-specific incidence rates re ported by the National Cancer Institute's Surveillance Epidemiology an d End Results Program. Standardized morbidity ratios (SMR) were calcul ated separately for regular and temporary employees. Results. Of the 2 8 cancers observed in the cohort, 12 were breast cancers. The SMR for breast cancer among regular female employees ranged from 2.55 (95% Cl : 1.31-4.98, P = 0.02) to 1.70 (95% Cl : 0.89-3.23, P = 0.09) dependin g on calendar year of follow-up, assumptions about completeness of fol low-up, and the reference rates used. The excess of breast cancer over expected in regular female employees diminished over time. No statist ically significant excess of breast cancer was noted for temporary fem ale employees at any point during follow-up. No increase in cancer inc idence was found over that expected for any cancer sites associated wi th ETO in previous studies-leukaemia, brain, pancreas and stomach. Con clusions. Factors such as appropriateness of latency periods, length o f follow-up and lack of a common histopathological type need to be con sidered in evaluating the excesses in observed breast cancer incidence , which diminished overtime.