Organochlorines and breast cancer: effect of exposure to dieldrin on risk and survival

Some organochlorines have weak estrogenic activity, and may therefore interfere with breast cancer risk and survival. We assessed prospectively risk and prognosis of breast cancer in relation to serum concentrations of several compounds, which have shown to be estrogenic in vitro and in vivo. Study participants (7712 women) donated blood twice (1976-1978 and 1981-1983) and were followed for 17 years with regard to development of breast cancer. Information on potential breast cancer risk factors and prognostics were obtained through standardized questionnaires and by linkage to the Danish Breast Cancer Cooperative Group.

Breast cancer risk associated with baseline exposure in 1976-1978, and repeated measurements of organochlorines (average concentration of the two measurements) was examined in two cohort-nested case-control studies, including 240 cases and 477 controls, and 155 cases and 274 controls, respectively. The cases served as a cohort in the survival analysis, in which the average duration of follow up to death was 86 and 79 months after the first and second sampling.

The most consistent finding observed was dieldrin's adverse effect on breast cancer risk as well as prognosis. More than a twofold increased risk was found among women with the highest baseline concentration compared with those with the lowest, and a significant trend was apparent. A high serum dieldrin concentration was also significantly associated with an increased overall mortality, being threefold for baseline measurements and almost sixfold when repeated measurements was assessed. Similar results were obtained when using breast cancer recurrence and/or death caused by breast cancer as end-point.