Desmoplastic amelanotic melanoma of palate: a case report with immunohistochemistry and electron microscopic studies.

A 24 year-old male with painful swelling over the right side of his palate for about two weeks was presented. An incisional biopsy was performed. In a routine hematoxylin and eosin examination by light microscopy, spindle and epithelioid cells with a bizarre appearance were discernible in the submucosal area. A pagetoid pattern was found in areas of the epithelium. Since this is not a remarkable finding, further examinations, such as the Trichrome-Masson and silver stain, immunohistochemistry using cytokeratin, vimentin, S-100, leukocyte common antigen, factor VIII, and alpha-1-antichymotrypsin detection kits, and electron microscopy were all carried out. According to the histological pattern of cells and the positive findings from the special stains, immunohistochemistry, and electron microscopy, a diagnosis of desmoplastic amelanotic melanoma was made. This variant of melanoma is a rare disorder with unremarkable, non-specific clinical manifestations in the oral cavity, which makes the diagnosis of this disease more difficult. We, therefore, report one case of this disease. Owing to the fact that diagnosis of this variant was mainly based on the positive findings of vimentin and S-100 in the immunohistochemistry examination and intracellular premelanosome detected by electron microscopy, immunodiagnosis and electron microscopy seem to be essential for differential diagnosis.