ERBB2 and breast cancer: Across the four HR/HER2-defined subtypes, the analyses of which were based on fewer cases than in the present study, statistically significant protective effects against HR-positive/HER2-negative breast cancer were detected (n = 341 cases), regardless of the duration of reported use (10+ years of use: relative risk (RR) = 0.66, 95% CI 0.49–0.89, fewer than 10 years of use: RR = 0.75, 95% CI 0.58–0.96).