Benign Breast Disease Increases Breast Cancer Risk Independent of Underlying Familial Risk Profile: Findings from a Prospective Family Study Cohort (ProF‐SC)

Benign breast disease(BBD) is an established breast cancer(BC) risk factor, but it is unclear whether the magnitude of the association applies to women at familial or genetic risk. This information is needed to improve BC risk assessment in clinical settings. Using the Prospective Family Study Cohort (ProF‐SC), we used Cox proportional hazards models to estimate hazard ratios(HRs) and 95% confidence intervals(CIs) for the association of BBD with BC risk. We also examined whether the association with BBD differed by underlying familial risk profile(FRP), calculated using absolute risk estimates from the BOADICEA model. During 176,756 person‐years of follow‐up (median: 10.9 years, maximum: 23.7) of 17,154 women unaffected with BC at baseline, we observed 968 incident cases of BC. A total of 4,704 (27%) women reported a history of BBD diagnosis. A history of BBD was associated with a greater risk of BC: HR = 1.31(95% CI: 1.14 ‐ 1.50), and did not differ by underlying FRP, with HRs of 1.35(95% CI: 1.11‐1.65), 1.26(95% CI: 1.00‐1.60), and 1.40(95% CI: 1.01‐1.93), for categories of full lifetime BOADICEA score <20%, 20% ‐ <35%, ≥ 35%, respectively. There was no difference in the association for women with BRCA1 mutations (HR: 1.64; 95% CI: 1.04‐2.58), women with BRCA2 mutations (HR: 1.34; 95% CI: 0.78‐2.3) or for women without a known BRCA1 or BRCA2 mutation (HR: 1.31; 95% CI: 1.13‐1.53) (p _interaction = 0.95). Women with a history of BBD have an increased risk of BC that is independent of, and multiplies, their underlying familial and genetic risk.

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