Natural killer-like T-cell lymphoma in a calf.

A case of natural killer (NK)-like T-cell lymphoma in a 9-month-old female Holstein calf is described. The liver, spleen and lymph nodes were affected with lymphoma. The neoplastic cells showed not only epitheliotropism in the biliary epithelium and hepatic cords but also preferential homing to follicular centres of the lymph nodes. In the cytoplasm, there were eosinophilic granules of various sizes, which were positive with phosphotungstic acid haematoxylin and naphthol AS-D chloroacetate esterase. Erythrophagia by lymphoma cells was rarely detected. Immunohistochemically, the neoplastic cells expressed surface CD3, surface CD5 and CD57, and perforin expression was present in the cytoplasmic granules. The lymphoma described resembled feline NK-like T-cell lymphoma in epitheliotropism in the liver and phagocytic activity but differed in respect of follicular involvement and marked variation in granule size.