Association of PIK3CA mutation with pCR and outcome by hormone receptor status and intrinsic subtype in early-stage HER2-positive breast cancer

PIK3CA mutations may be associated with outcomes of patients with HER2-positive early breast cancer (EBC). A cohort study using data on 184 patients from the phase 3 neoadjuvant CALGB 40601 trial investigated the association of PIK3CA mutations with response to therapy and outcomes among patients with HER2-positive EBC, and the impact of hormone receptor (HR) status and intrinsic molecular subtype on this association. PIK3CA mutation was associated with lower pathologic complete response rate to chemotherapy plus trastuzumab, and with independently worse event-free survival, owing to the HR-positive and luminal intrinsic subtypes. The authors conclude that this study suggests that PIK3CA mutations, which are therapeutically targetable, are associated with response to therapy as well as outcome in HER2-positive EBC, particularly luminal disease.