Diagnostic approach to malignant fibrous histiocytomas of soft tissue in dogs: a case report

Malignant fibrous histiocytomas (MFHs), newly named as ‘undifferentiated pleomorphic sarcomas’ in 2002 by the World Health Organization, generally show an ambiguous origin. They have been described to fibroblastic or histiocytic in origin, while storiform-pleomorphic variants share a similar morphologic pattern with other sarcomas. For this reason additional diagnostic methods including immunology, ultrastructure analysis and molecular approaches are necessary for a more accurate diagnosis. We report three cases of MFH in individual dogs which presented histological characteristics of pleomorphic sarcomatoid tumours. Microscopic investigation, immunohistochemistry (vimentin, CD68, desmin, α-smooth muscle actin, and S-100) and electron microscopy were performed for diagnosis. One case was diagnosed as storiform-pleomorphic type and two were diagnosed as giant cell type MFHs. The present study demonstrates concepts of MFHs based on newly described categories and suggests useful diagnostic approaches for uncertain sarcomatoid soft tissue tumours in canines.