To exclude that the immunoreactive cells were actually neoplastic, double-label immunohistochemistry for Sox2 and CD20 (for NHL-CNS), Sox2 and cytokeratin (CAM5.2, for carcinomas), or Sox2 and HMB45 (for melanomas) showed that in each tumor type, Sox2-immunoreactive cells adjacent to and among the tumor cells were separate from neoplastic cells. This evidence concerns the gene PMEL and melanoma.