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Nevoid Melanoma

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Nevoid melanoma is a rare subtype that mimics and is often misdiagnosed as a benign nevus at low magnification. Clinically, it presents as verrucous lesion or dome-shaped nodule with variable pigmentation. The verrucous lesions are poorly-circumscribed and asymmetrical with marked hyperkeratosis and papillomatosis. In nodular lesions, the epidermis is stretched thin over the tumor with loss of rete ridges. Junctional activity is minimal to absent.

The infiltrating tumor cells are arranged in sheets or nests and consist of small epithelioid melanocytes resembling type A nevus cells. They have pale or eosinophilic cytoplasm, round to oval vesicular nuclei, and small punctate nucleoli. Mild to moderate nuclear pleomorphism is seen and mitotic activity is increased, especially in the deeper portions of the tumor. Uncommonly seen features include pigmentation, tumor-infiltrating lymphocytes, and perineural invasion.

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