In a 48-year-old woman with primary amelanotic melanoma of the left palm resembling tylosis clinically and nevus of large spindle and/or epithelioid cells pathologically, electron microscopy showed stage III melanosomes in the cytoplasm of the tumor cells. Histologically, the tumor cells formed alveolar structure or nests at the dermo-epidermal junction and showed pagetoid phenomenon to the upper epidermis and to the lateral or radial individual cell extension. Most of the tumor cells lacked melanin pigment on light microscope. A large number of giant cells, telangiectasis and edema of the dermal papilla made it difficult to differentiate this melanoma from nevus of large spindle and/or epithelioid cells. Differentiation between these two melanocytic lesions were discussed on the basis of the related literature.
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