Malignant melanoma in albino water buffalo (Bubalus bubalis)

Two albino water buffalo affected by multiple melanocytic tumors in Southern Brazil are described. Grossly, there were multiple dark tumors within the skin, skeletal muscle, lungs, and lymph nodes. The tumor was also present in the pericardial sac, renal capsule, mediastinum and pleura. Microscopically, the tumors consisted of polyhedral epithelioid cells arranged in solid nests or interwoven fascicles supported by a thin and sparse collagenous stroma. The cytoplasm was eosinophilic and sometimes contained varying amounts of melanin pigment. The mitotic rates were low. Immunohistochemistry staining with Tyrosinase, Melan-A, Vimentin, S-100 protein, and neurofilament were positive. It is possible that the polymorphisms related to pigmentation in albino buffalo contributed with a high risk of developing melanoma as suggested in humans.