ERBB2 and breast cancer: Furthermore, in this cohort, the proportion of HER2-low cases in breast cancer samples with residual tumours after neoadjuvant therapy was lower than in breast cancer primaries, and the decrease in HER2-low cases in residual tumours after neoadjuvant therapy compared with breast cancer primaries was mainly due to the fact that HER2-low cases switched to HER2-zero with treatment.