In particular, among patients preserving HR-positive/HER2-negative BC subtype during disease evolution, those with HER2-low expression on primary tumor experienced significantly poorer PRS and OS as compared to patients with HER2-0 primary BC (HER2-0 vs HER2-low: median PRS 53.2 vs 41.7 months, respectively, hazard ratio 0.71 (95% CI 0.53-0.96), p = 0.025; median OS 128.2 vs 100.3 months, respectively, hazard ratio 0.72 (95% CI 0.54–0.97), p = 0.030). Here, ERBB2 is linked to breast cancer.