A prospective study on corpus luteum function and breast cancer risk.

A case-control study incorporated within a cohort study was undertaken to test the hypothesis that anovulation or decreased luteal function is associated with increased risk of breast cancer. A large population (n = 12,000) of apparently healthy women aged 40-49 collected a specimen of urine on day 22 of 3 consecutive menstrual cycles, or, in cases of amenorrhea, on 3 arbitrarily chosen days. These samples were stored at -20 degrees C. Subsequent screening of the women by mammography revealed 34 cases of breast cancer, and over the next 4 years a further 34 cases were reported to the cancer registry. Urine samples from 53 of these cases were assayed for pregnanediol and creatinine, and the results were compared with those for an equal number of matched controls. No differences between these groups were found in the pregnanediol/creatinine ratio. We conclude that our results do not support the hypothesis that women with luteal insufficiency are at increased risk for breast cancer. However, since breast cancer patients tend to have a later menopause than controls, the possibility cannot be excluded that breast cancer patients continue to have ovulatory cycles for a longer period during reproductive life. Such a finding--opposite to the working hypothesis--would complicate the interpretation of the results.