On microscopic examination, the tumor is characteristically composed purely of epitheloid cells and absent of fat cells and the blood vessels.[6] Unlike the typical PEComa, which co-expresses melanocytic markers (HMB-45, HMB50, Melan-A) and smooth muscle markers (smooth muscle actin, muscle specific actin, calponin), the pigmented PEComa of kidney distinctively exhibits immunohistochemical reaction with HMB-45 but hardly with muscle markers. This evidence concerns the gene MLANA and neoplasm.