ERBB2 and breast cancer: Rates of HER2-positive, HER2-low and HER2 0 BC in all available unmatched samples and stratified according to ER status, at primary disease, residual disease following NAT and at metastatic biopsy, as well as for patients with biopsies from all three timepoints (primary, residual and metastatic disease), are shown in Supplementary Fig. 1.