Malignant fibrous histiocytoma (giant cell type) associated with a malignant mixed tumor in the salivary gland of a dog

A 12-year-old male Boxer dog presented with a 5 X 5 X 7-cm partially encaps ulated mass in the right mandibular salivary gland. Histologically, the mas s was composed of neoplastic epithelial and mesenchymal cells. The mesenchy mal component consisted of two cell populations arranged in different patte rns: coalescing nodules of neoplastic mononuclear cells with rare osteoid a nd numerous osteoclastlike giant cells; and sheets of neoplastic spindle ce lls intermingled with neoplastic epithelial cells and containing osteoid an d well-formed bone trabeculae lined by osteoblasts and few osteoclastlike g iant cells. On the basis of these histological features, two malignant sali vary tumors were diagnosed: a malignant fibrous histiocytoma (giant cell ty pe! and a malignant mixed tumor. Immunohistochemical studies demonstrated k eratin 5 and 8 expression by the neoplastic epithelial cells, indicating a probable salivary ductal origin, and vimentin expression by all mesenchymal elements, suggesting a fibroblastic line of differentiation.