PIK3CA and esophageal squamous cell carcinoma: To have a better understanding on the drug mechanism, Zhang et al. established a panel of patient-derived tumor xenograft models and well characterized them for common genetic aberrations frequently detected in ESCC, such as HER2 expression and mutations of EGFR (epidermal growth factor receptor), K-ras, B-raf and PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha).