<i>PIK3CA</i> Mutations Are Associated With Lower Rates of Pathologic Complete Response to Anti–Human Epidermal Growth Factor Receptor 2 (HER2) Therapy in Primary HER2-Overexpressing Breast Cancer

HER2-positive breast carcinomas with a PIK3CA mutation are less likely to achieve a pCR after neoadjuvant anthracycline-taxane-based chemotherapy plus anti-HER2 treatment, even if a dual anti-HER2 treatment is given.