Retrospective assessment of menstrual cycle length in patients with breast cancer, in patients with benign breast disease, and in women without breast disease.

The length of the menstrual cycle was compared in women with breast cancer, women with benign breast disease, and controls. Older women in general tended to report shorter menstrual cycles (P less than 0.05). After correction for the age difference, breast cancer patients still reported a shorter average menstrual cycle length than benign breast disease patients and controls (P less than 0.006). Very short cycles (less than or equal to 21 days) were present in 20% of the breast cancer patients compared to 8% of the patients with benign breast disease and 4% of the controls (P less than 0.0001). Long cycles (less than or equal to 30 days) were not a feature of breast cancer patients (2%), whereas 20% of the patients with benign breast disease and 20% of the controls reported such long cycles (P less than 0.0001). Irregular menstrual cycles were more common in benign breast disease patients (20%) than in cancer patients (10%) and controls (8%) (P less than 0.001).