A schirrhous anaplastic carcinoma in two dogs resembling mesothelioma.

The clinical, laboratory, radiographic and pathological findings of two dogs with similar neoplasms are described. Both dogs were mature males of a large breed and had pleural and abdominal effusions containing neoplastic cells. Diffuse scirrhous thickening of the pleura and serosal surfaces was a prominent feature. A fibrous layer containing nests of neoplastic, epithelial-like cells was present on serosal surfaces. The morphological appearance of the cells was suggestive of either an atypical sclerosing mesothelioma or a scirrhous carcinoma. On the basis of ultrastructural and differential staining characteristics, a diagnosis of a scirrhous carcinoma of undetermined primary origin was made in one case and of prostatic urethral origin in the other case.