PIK3CA and breast cancer: Compared to the somatic alteration profiles of other BC subtypes, TNBC had significantly lower mutation frequency in PIK3CA (TNBC vs. HRPBC, p = 0.009), but higher mutation frequency in TP53 (TNBC vs. HRPBC, p = 0.036; TNBC vs. HHPBC, p = 0.004).