Histocytology of lymphoid tumors in the dog, cat and cow.

In a retrospective study of lymphomas in animals, tumors in 72 dogs, 81 cats and 90 cows were classified on the basis of cell size (small, medium and large), nuclear cleavage (follicular center cells), and histologic architecture (nodular or diffuse). Each subtype was classified by age of animal at death, number of metastases, breed, and sex. As in man, nodular cleaved tumors are rare in animals, the cow having the most varied tumor types. There was one cleaved-cell tumor in 72 lymphomas in dogs, 23 of 81 in cats, and 33 of 90 in cows. There were six nodular tumors of 72 in dogs, two of 81 in cats and eight of 90 in cows. Fifteen of 16 nodular lymphomas had noncleaved cells and twelve had small or predominantly small cells. Cats with nodular lymphomas were older at death than cats with diffuse lymphomas. Nodularity was not associated with greater age at death in dogs and cows. Animals with cleaved-cell lymphomas were older at death than those with noncleaved tumors; this difference was highly significant in cows. The number of metastases was greater with nodular tumors in all three species, and was equal in cleaved and noncleaved tumors. The biological behaviour of lymphoid tumors in animals is similar to those in man when the same criteria of classification are used.