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Melanocytic Tumors of the Skin: A Dermatopathological Review

Ish Pandhi, Shashi Bhushan Pandhi, Sunil Alipuria Pandhi, and Sonam Ish Pandhi

Diagnosis of melanocytic tumors poses two big problems for a histopathologist, firstly to diagnose it as melanocytic tumor and the other important problem is the determination of whether the lesion of obvious melanocytic nature is benign or malignant. Here we wish to provide few key histopathological features of some important tumors that will guide a histopathologist in overcoming these problems. Melanocytes are generally positive for melanin stains (such as the Fontana- Masson silver stain), tyrosinase, DOPA reaction, S-100 protein, NSE, Mart-1/MelanA (A103), microphthalmia transcription factor, Sox10 (a neural crest transcription factor) PAX3 (a transcription factor with an important role in the development of melanocytes during embryogenesis), and vimentin; the intensity of these reactions shows marked variability, possibly depending on the functional status of the cell.1 Stains for neurofilaments and glial fibrillary acidic protein are negative. Stains for HMB-45 are generally negative in normal resting melanocytes but positive in activated melanocytes, including those of malignant melanoma. Keratin is another marker that is consistently absent in normal melanocytes but sometimes expressed in their neoplastic counterpart. The fact that normal melanocytes show strong immunoreactivity for the BCL2 proto-oncogene product has been recorded. This is also expressed in benign nevi and less commonly in malignant melanomas. Though it is a challenge for a histopathologist to make a specific diagnosis of a case of melanocytic tumor but with clinical correlation and step by step approach aided with IHC, most of the tumors can be diagnosed correctly. Staging of the tumors is obviously done after proper consultation with dermatologist