Plasma organochlorine levels and subsequent risk of breast cancer among Japanese women: a nested case-control study.

To our knowledge, no prospective study has examined the association between blood levels of organochlorines and breast cancer risk in Asian countries. Here, we tested the hypothesis that higher blood levels of organochlorines are associated with an increased risk of breast cancer in Japanese women. A total of 24,226 women subjects of the Japan Public Health Center-based Prospective Study aged 40 to 69 years who responded to the baseline questionnaire and provided blood in 1990-1995 were followed to December 2002. During 10.7 years follow-up, 144 cases of breast cancer were newly diagnosed. Two matched-controls for each case were selected from the cohort. Plasma levels of p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), hexachlorobenzene (HCB), and beta-hexachlorocyclohexane (beta-HCH) were measured. A conditional logistic regression was used to estimate the odds ratio (OR) of breast cancer according to cholesterol-adjusted organochlorine levels based on 139 matched pairs. We found no statistically significant positive association between plasma organochlorine level and breast cancer risk. Adjusted ORs for p,p'-DDT, HCB, and beta-HCH were less than 1. For p,p'-DDE, adjusted OR for the highest versus lowest quartile was 1.48 (95% confidence interval 0.70-3.13; p for trend=0.25). A stratified analysis by menopausal status showed positive associations for p,p'-DDT and p,p'-DDE in premenopausal but not postmenopausal women, although without statistical significance. Our data do not support the hypothesis that plasma levels of p,p'-DDT, p,p'-DDE, HCB, and beta-HCH are associated with an overall increased risk of breast cancer among Japanese women.