ERBB2 and breast cancer: In ERBB2/HER2-positive early breast cancer (EBC), neoadjuvant treatment is now the standard of care given the surgical benefits of tumor downstaging1 and the benefits of tailoring adjuvant anti-ERBB2/HER2 drugs based on the presence of residual disease at surgery.2 Pathologic complete response (pCR) at surgery has been associated with improved survival,3 but a predictable quantitative relationship between pCR benefit and survival outcomes has been elusive.