The HER2-positive/HR-positive substudy of the three-arm, phase II–III Adjuvant Dynamic Marker-Adjusted Personalized Therapy Trial Optimizing Risk Assessment and Therapy Response Prediction in Early Breast Cancer (ADAPT) (NCT01779206) [18] has shown substantial pCR rates (no invasive tumor in the breast and lymph nodes) of ~40% after only 12 weeks in both T-DM1 study arms (with or without ET), compared to ~15% after trastuzumab plus ET. Here, ERBB2 is linked to breast cancer.