Malignant fibrous histiocytoma in a dog.

A large tumour present on the proximal tibia of a Bull Mastiff dog was diagnosed on histological appearance as a Malignant Fibrous Histiocytoma. These tumours, rarely identified in domestic animals, but well recognised in humans, are typically pleomorphic sarcomas with histiocytic and fibroblastic differentiation. Less commonly, one cell type predominates. In this case there was prominent histiocytic differentiation.