Mast cell sarcoma with megakaryocytic differentiation in a calf.

A case of mast cell sarcoma in a 5-month-old Holstein female calf is described. Macroscopically, enlargement of the spleen, lymph nodes, tonsils and kidneys was noted, and there were tumor masses in the neck region and on the pleura and peritoneum. The pericardium and uterine and ureter walls were also involved by tumor. Most neoplastic cells had eosinophilic granules, which were metachromatic and positive for naphthol AS-D chloroacetate esterase and tryptase, whereas smaller numbers of cells were positive for factor VIII-related antigen, a marker of megakaryocytes. Some of the predominant type of these tumor cells were found within the epithelia of the lungs, tonsils, gastrointestinal tract, liver, ureters, urinary bladder and uterus. Their normal counterparts were considered to be globule leukocytes.