PIK3CA and cancer: Akin to HER2E tumors, disregarding ERBB2 amplifications, the mutational and amplification landscape of cancer drivers within HER2p-HER2E tumors was mainly characterized by high frequencies of predominantly missense mutations in PIK3CA (38.7%) and TP53 (68.2%), as well as MYC amplifications (38.6%), thereby further corroborating the similarities between HER2E and HER2p-HER2E tumors (Fig. 5J).