Risk factors for benign breast disease: a 30-year cohort study.

Data on the menstrual history, family history and degree of obesity of 1374 Vancouver nursing students were collected in 1945 and from 1947 to 1956. In 1979, 768 of these women were located; 726 (94%) responded and participated in a follow-up study, providing information on their subsequent medical history and on breast-related problems. No major differences were found between the early histories of these participants and those who were not located or did not respond. Among the respondents 215 gave a history of symptoms compatible with benign breast disease; in 107 this diagnosis was confirmed by biopsy. By age 50 the cumulative risk for benign breast disease was 17% for biopsied and 31% for symptomatic disease. Biopsied benign breast disease was associated with premenstrual breast discomfort, irregular menses, a history of abortions, a family history of both benign and malignant breast disease, lack of use of oral contraceptives, a low index of obesity and small breasts, obesity and breast size being independent. Factors associated with symptomatic benign breast disease were usually associated with a greater likelihood of biopsy for symptomatic disease; hence, the relative risks for biopsied disease were generally greater than those for symptomatic disease. Although the risk factors for benign breast disease differ from those for breast cancer, the findings are consistent with the hypothesis of excessive circulating estrogen.