PIK3CA and breast cancer: The PIK3CA mutation frequency significantly differed among the four breast cancer molecular subtypes, with 48.3% (155/321) in HR+/HER2-, 45% (50/111) in HR+/HER2+, 42.2% (27/64) in HR-/HER2+, and 25% (17/68) in HR-/HER2- patients (Table 1).