ERBB2 and aneurysmal bone cyst: To investigate the mechanisms underlying lower T-DM1 efficacy following trastuzumab/pertuzumab in ABC patients, we established trastuzumab (T), pertuzumab (P), and trastuzumab+pertuzumab (T + P)-resistant HER2+ SkBr3 and BT474 cell lines (Fig. 1a).