ERBB2 and neoplasm: Clinical trials based on CAR targeting single antigens, such as human epidermal growth factor receptor 2 (HER2) (42), mesothelin (MSLN) (43), prostate stem cell antigen (PSCA) (44) are found mixed results due to the loss of tumor antigen on tumor cells, which confirms a fundamental issue with CAR T cell therapies: a lack of ideal single antigen targets.