ERBB2 and breast cancer: Standard-of-care predictive markers in breast cancer include activating PIK3CA mutations (in hormone-receptor-positive metastatic breast cancer), which were reported in 37.1% of samples, with most (3779/4082, 92.6%) occurring in the absence of ERBB2 amplification; other predictive markers include inactivating BRCA1/2 alterations (9.4%) and ERBB2 amplification (7.6%) (Table 3).