Spindle Cell Melanoma Harboring a Nodule of Epitheloid Cell Melanoma Component: A Study of a Diagnostically Challenging Case

Abstract Background: Melanoma is a very heterogeneous human neoplasm. In addition to four major (conventional) histologic subtypes a number of uncommon variants do exist. Objective: An unusual case of a spindle cell melanoma (SCM) containing a demarcated nodule of conventional epitheliod cell melanoma component is described. Material and Methods: A 71-year-old man manifested with a protuberated ulcerated skin tumor arising on the right forearm. The resected biopsy was analyzed immunohistochemically with a variety of anti-human antibodies. Results: The tumor consisted of a highly cellular mass of spindle-shaped cells without any significant intratu-moral fibrosis. In addition, a nodule of epithelioid cell tumor component was present within the lesion. The spindle cell component showed a disperse reactivity for S100 protein and was negative for other melanocytic markers. It exhibited a very high mitotic activity and proliferation Ki-67 index. No melanin pigment was detected. In contrast, the epithelioid cell component was strongly positive for S100 protein, Melan-A/MART-1, HMB-45, and PNL-2. The mitotic and proliferation indices were much less pronounced and melanin deposits were visible. A diagnosis of a non-desmoplastic SCM harboring a nodule of epithelioid cell melanoma component was established. Conclusion: SCM often posses a diagnostic dilemma because its histomorphology is atypical and its immunohistochemical profile may differ from other subtypes of melanomas. The present paper points out this uncommon histopathological entity that may sometimes be encountered in dermatopathological practice and that requires more complex diagnostic approach.