Oral contraceptives and reduced risk of benign breast diseases.

In 1970 a questionnaire on oral-contraceptive use was mailed to 97,254 married women 25 to 49 years of age in Greater Boston. Sixty-nine per cent responded. During the subsequent 30 months, 1072 of the women were hospitalized for breast diseases. Hospitalization rates for fibrocystic disease were similar for non-users of oral contraceptives and users of one to 12 months' duration. However, users for 13 months to 24 months and 25 or more months had rates only 70 and 35 per cent, respectively, of those of non-users. Detailed analysis of these results, and their similarity to findings in previous studies, suggest that the association is causal--use of oral contraceptives appears to lower risk of fibrocystic breast disease. A similar association was seen for fibroadenoma. Rates of breast cancer were lower for users than for non-users, but this finding was neither related to duration of use nor statistically significant.