PMEL and neoplasm: A criticism of cancer vaccines as an approach for tumor immunotherapy is that the tumor antigens that have been targeted to date are often (in the case of tumor-associated antigens, e.g., the melanocyte differentiation antigen gp100 or mesothelin) but not always (in the case of cancer-testes antigens, e.g., NY-ESO) derived from proteins expressed in the periphery by healthy cells.