PIK3CA and esophageal squamous cell carcinoma: By establishing a patient-derived xenograft (PDX) model in nude mice, Wu X et al. [91] demonstrated that ESCC tissues harboring PIK3CA mutations were insensitive to trastuzumab, a type of humanized monoclonal antibody used to treat breast cancer and gastric cancer, which has been infrequently used for ESCC.