ERBB2 and breast cancer: Chemotherapy can shrink HR-positive breast tumors and make more favorable surgical options available, but it is less likely to achieve pCR in HR-positive breast cancers, especially luminal A cancers, than in more proliferative histologies.2,50 Among those with HR-positive, ERBB2-negative disease, the percentage of patients with pCR after NACT was reported to be between 8% and 16%, depending on tumor differentiation,16,17 which is compatible with our identified rate (12.5%) (eTable in the Supplement).