ObjectiveTo analyze the risk of breast cancer in women who underwent pelvic surgery in premenopause using data from two case-control studies conducted between 1983 and 1994 in six Italian centers.MethodsSubjects were 5984 women with histologically confirmed breast cancer diagnosed within the year before interview who were admitted to the major teaching and general hospitals in the areas included in the studies. Controls were 5504 women who resided in the same geographic areas and were admitted for acute conditions to the same network of hospitals in which cases had been identified. Women were not included if they had been admitted for gynecologic, hormonal, or neoplastic disease.ResultsA total of 719 cases (12% and 801 controls (15%) underwent pelvic surgery before menopause. The risk of breast cancer was reduced in women who underwent bilateral oophorectomy with hysterectomy (odds ratio [OR] adjusted for age, calendar year at interview, study, and center, 0.8, 95% confidence interval [CI] 0.7, 0.9) and hysterectomy alone (OR 0.7, 95% CI 0.6, 0.8). The protection tended to increase with time since surgery, but no relationship emerged when age at menopause was included in the analysis. No clear relationship emerged between time since unilateral oophorectomy with or without hysterectomy or since hysterectomy alone and breast cancer risk.ConclusionThe risk of breast cancer is lower in women who undergo bilateral oophorectomy before menopause, and the protection increases with time from surgery.