Abstract

This report describes a primary malignant melanoma which developed in the anus, as documented by light microscopy and immunohistochemistry. A 53-year-old woman had a 4 month history of a protruding mass in the anal canal. The mass was located in the squamo-columnar junction of the anal canal, measuring 5.0x4.5 cm. Its cut surface was dark brown and poorly circumscribed. The histologic appearance was characterized by epithelioid or spindle cells with prominant nucleoli and frequent atypical mitosis. Melanin pigments were strongly seen in Fontana-Masson stain. Immunoreactivity revealed that the cytoplasm of tumor cells was strongly positive with antibody directed against S-100 protein, vimentin and it was focally positive with neuron specific enolase.

• Keywords: Malignant melanoma;Anus