Pathomorphological and immunohistochemical studies on melanocytic tumors in cattle

The present study was carried out to know the occurrence and pathomorphology of melanocytic tumors viz. melanocytoma and malignant melanoma in cattle. Out of 29 tumors of cattle collected during a period of 2 years, five melanocytic tumors (17.4%) were recorded in the present study. Grossly, the tumors were 3 to 10 cm in diameter, solitary, circumscribed to multinodular, sessile to pedunculated, soft to firm with variegated greyish white to black appearance. Cytology revealed clusters of pleomorphic melanocytes containing large nuclei and variable amounts of melanin granules in the cytoplasm. Histologically, melanocytoma revealed sheets of neoplastic melanocytes containing variable amounts of melanin granules obscuring the nuclear morphology while, malignant melanomas were characterized by the presence of nests of amelanotic to melanotic cells separated by a thin fibrovascular stroma located in the dermis. On IHC, all the melanocytic tumors were positive to S100.