Pertuzumab was approved for metastatic disease based on the phase III CLEOPATRA trial, which randomized 808 previously untreated patients to receive dual HER2 blockade with trastuzumab/pertuzumab/docetaxel or trastuzumab/docetaxel/placebo (Swain et al., 2015). This evidence concerns the gene ERBB2 and metastatic neoplasm.