Like extrarenal rhabdoid tumors, melanomas with rhabdoid features show large epithelioid cells with eosinophilic hyaline intracytoplasmic inclusions. These inclusions are composed of aggregates of intermediate filaments. The tumor cells have vesicular nuclei and prominent eosinophilic nucleoli. Note the histologic overlap with signet ring cell melanoma.
The expression of melanoma markers (HMB-45, S-100 protein, and MART-1) is variable. Some tumors are positive; others may be negative for these markers but show immunoreactivity for keratin, SMA, or desmin in the inclusions. Given the rarity of this variant, it is not known whether rhabdoid phenotype is an independent adverse prognostic factor.