ERBB2 and breast cancer: PIK3CA mutations were increased overall in metastatic vs. primary sites (32.1 vs. 26.9%, p < 0.0001), specifically in HR-positive HER2-positive breast cancer (44.1 vs. 25.2%, respectively, p = 0.002) and TNBC (21 vs. 14.3%, respectively, p = 0.0002).