Background: Despite the endocrine system activity exhibited by polychlorinated biphenyls (PCBs), recent studies have shown little association between PCB exposure and breast cancer mortality. Objectives: To further evaluate the relation between PCB exposure and breast cancer risk, we studied incidence, a more sensitive endpoint than mortality, in an occupational cohort. Methods: We followed 5,752 women employed at least a year in one of three capacitor manufacturing facilities, identifying cases from questionnaires, cancer registries, and death certificates through 1998. We collected lifestyle and reproductive information via questionnaire from participants or next of kin and used semi-quantitative job-exposure matrices (JEMs) for inhalation and dermal exposures combined. We generated standardized incidence ratios (SIRs) and standardized rate ratios (SRRs) and used Cox proportional hazards regression models to evaluate potential confounders and effect modifiers. Results: Overall, the breast cancer SIR was 0.81 (95% CI 0.72, 0.92, n=257), and regression modeling showed little effect of employment duration or cumulative exposure. However, for the 362 women of questionnaire-identified races other than white, we observed positive, statistically significant associations with employment duration and cumulative exposure; only smoking, birth cohort, and self or proxy questionnaire completion had statistically significant explanatory power when added to models with exposure metrics. Conclusions: We found no overall elevation in breast cancer risk following occupational exposure to PCBs. However, the exposure-related risk elevations seen among non-white workers, while of limited interpretability given the small number of cases, warrant further investigation, as the usual reproductive risk factors accounted for little of the increased risk.
Sharon R. Silver, M.S., Industrywide Studies Branch, DSHEFS, NIOSH, 4676 Columbia Parkway, R-15, Cincinnati, Ohio 45226