Moreover, there is no established positive predictive value for HMB-45 staining in the diagnosis of nevoid melanoma; also some nevi (i.e., deep penetrating nevi, blue nevi and fibrotic dysplastic nevi) show diffuse (i.e., non-gradient) expression of HMB-45 from top to bottom [14, 34]. This evidence concerns the gene PMEL and dysplastic nevus.