Cyclic ovarian function and breast cancer.

We postulated previously that systematic differences in menstrual cycle length and/or variability might be used as indicators of underlying hormonal abnormalities that could help explain the endocrine biology of some breast cancer risk factors. In the present study, we prospectively and retrospectively analyzed menstrual cycle patterns in breast cancer cases and controls in two populations. No significant differences were found. This and previous studies emphasize that contemporary women have a long reproductive experience characterized by uninterrupted, regular menses, which is a condition of maximum ovulation potential and which contributes to estrogen stimulation over time.