MLANA and neoplasm: Immunohistochemically, the tumor cells, including signet-ring cells, were diffusely positive for S-100 protein, vimentin and Melan-A (Fig. 1B), but negative for HMB-45, cytokeratin (AE1/AE3 and CAM5.2), nestin, peripherin, α-internexin and GFAP.