ERBB2 and breast cancer: Compared with HER2-zero tumours, HER2-low BC had significantly better RFS (centre-adjusted HR 0.88, 95% CI 0.82–0.93, P < 0.001) and OS (centre-adjusted HR 0.82, 95% CI 0.76–0.89, P < 0.001) (Fig. 1A, B).