PIK3CA and breast cancer: These mutations were chosen because of their known roles in breast carcinogenesis (e.g., mutations in PIK3CA), likelihood to impact targeted therapies currently being explored in breast cancer (e.g., mutant PIK3CA impacts resistance to HER2 targeted therapies; and mutations in key genes of the MAP kinase pathway that impact resistance to EGFR-targeted therapies (e.g., KRAS, HRAS, and BRAF)), or their potential as a therapeutic target (e.g., PIK3CA and BRAF mutant proteins).