Breast cancer risk after hysterectomy with and without salpingo-oophorectomy for benign indications

Breast cancer risk has been extensively studied in women with genetic predisposition, i.e. BRCA1/2. Though there are guidelines for performing bilateral salpingo-oophorectomies in individuals with specific genetic risks, oophorectomies are also performed in many average-risk women. The risk of breast cancer in average risk women who undergo hysterectomy with bilateral salpingo-oophorectomy for benign indications is less clear. We aim to estimate breast cancer risk following hysterectomy with and without concomitant bilateral salpingo-oophorectomy for benign indications. From 2001 to 2015, women aged 18 and older from Kaiser Permanente Northern California who underwent hysterectomy alone and hysterectomy with bilateral salpingo-oophorectomy were identified using ICD-9 procedure and CPT codes. Women with a BRCA mutation and prior history of breast or gynecologic cancer were excluded. Descriptive and bivariate analyses were used to describe and compare demographic and clinical characteristics. Breast cancer incidence rates were calculated per 100,000 person-years. Survival analysis and Cox proportional hazard models were conducted to compare risk of developing breast cancer. Of 49,215 women who underwent hysterectomy, 19,826 had hysterectomy with bilateral salpingo-oophorectomy. Whites comprised 51.2%, Hispanics 20.3%, Blacks 12.7%, Asians 10.4%, and other/unknown 5.3% of the study population. The average age of women with hysterectomy only was 45.5 compared to 50.8 with hysterectomy with bilateral salpingo-oophorectomy. During the study period, 915 women were diagnosed with breast cancer. Age-specific breast cancer incidence rates were higher in women over 60 with oophorectomy compared with hysterectomy alone (471.2 [95% CI 386.2-556.2] vs. 463.0 [95% CI 349.6-576.5], respectively). After controlling for age, race, income, and Charlson comorbidity index, women with bilateral salpingo-oophorectomy had a 14% lower risk of breast cancer compared with women with hysterectomy only (HR=0.86, 95% CI 0.75-0.98). All-cause mortality was higher with oophorectomy versus hysterectomy only (64.4% vs. 35.6%, p

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