Abnormal expression of gene products commonly caused by amplification/mutation of HER2 and PIK3CA in high-grade serum endometrial cancer (USC) and ovarian cancer (HGSOC) and PIK3CA mutations are likely results of afatinib resistance, which can be overcome by HER2 combined with PIK3CA, AKT, or MTOR inhibitors. The gene discussed is PIK3CA; the disease is ovarian cancer.