Thymic carcinoma of the thymic hormone secretory type in a cow

An 8-year-old Holstein cow had tumor nodules and enlarged lymph nodes in th e mediastinum, and metastatic tumor masses in the pelvic cavity. The neopla stic cells were characterized by squamous features and intracytoplasmic vac uoles carrying microvilli, some of which contained periodic acid Schiff-pos itive globular cores, but tubular structures or goblet cells were absent. M any neoplastic cells stained positively for keratin, and occasional cells w ere positive for thymosin. The presence of secretory granules in the cytopl asm was confirmed by electron microscopy. This neoplasm was considered to b e of thymic hormone-secreting epithelial cell origin.