A neoplasm of globule leukocytes in a cat

A neoplasm involving the ileo-cecal-colic junction, thymus, and tracheobronchial lymph nodes of a 7-year-old domestic cat was composed of dense sheets of round to oval mononuclear cells with oval to indented nuclei, moderate amounts of cytoplasm, and variable numbers of round eosinophilic granules. These granules are brown to black in phosphotungstic acid hematoxylin-stained sections and stain variably with the periodic acid-Schiff stain. They are 0.8 to 1.5 micron in diameter, limited by a single unit membrane, and have variable electron density. Light microscopic cellular morphology and staining characteristics as well as ultrastructural features of these cells are consistent with feline globule leukocytes. Morphologic features of the neoplastic cells in the present case are similar to those of the only other reported neoplasm of globule leukocytes which also involved the intestine of a cat.