PIK3CA and invasive breast carcinoma: PIK3CA was the second most frequently altered gene, with mutations found in 19.8% of patients (2,750 of 13,880), occurring most frequently in uterine corpus endometrial carcinoma (53.5%), ovarian endometrioid adenocarcinoma (49.0%), breast invasive carcinoma (42.2%), uterine corpus endometrial serous carcinoma (38.1%) and colon adenocarcinoma (26.5%).