PIK3CA and neoplasm: Importantly, type I PI3K inhibitors potently reduce growth of HER2+ tumor cells in culture and in vivo, and combinations of type I PI3K and HER2 inhibitors display superior anti-tumor activity against HER2+ cancers, suggesting that multiple signaling nodes in the HER2/PI3K pathway require inhibition to abrogate feedback PI3K re-activation that often occurs in response to single-agent inhibition [8–13].