ERBB2 and breast cancer: In the hormone receptor-negative subgroup, HER2-low BC had a non-significant trend towards better RFS (centre-adjusted HR 0.92, 95% CI 0.81–1.05, P = 0.226) and significantly longer OS (centre-adjusted HR 0.82, 95% CI 0.69–0.96, P = 0.017) than HER2-zero BC (Fig. 1E, F).