These features were the macroscopic appearance, the combination of dermal and plexiform presentations, alternating areas of hyper- and hypo-cellularity, strong S100b positivity, the presence of mast cells, collagen bundles, and hyalinized vessels, and the upregulation of Schwann cell–specific gene expression compared with those in the intradermal melanomas. The gene discussed is S100B; the disease is melanoma.