IMMUNOHISTOCHEMICAL STAINING OF FELINE MALIGNANT FIBROUS HISTIOCYTOMAS

Malignant fibrous histiocytoma was diagnosed in seven cats from biopsy specimens received at the University of Missouri Veterinary Medical D iagnostic Laboratory during a 4-year period from 1987-1991. Tissue blo cks from formalin-fixed specimens were resectioned and stained for typ e I (AE1) and type II (AE3) cytokeratins, desmin, S100 protein, viment in, and alpha(1)-antitrypsin by the avidin biotin peroxidase complex m ethod with diaminobenzidine (DAB) chromogen. None of the tumors staine d positively for alpha(1)-antitrypsin. Four of seven of the tumors had similar immunohistochemical staining results, with positive staining for type I and type II cytokeratins, desmin, S100 protein, and vimenti n. Of the remaining three, one stained positively only for S100 protei n and vimentin; one stained positively for vimentin only; and one was negative for all six antigens. Based only on immunohistochemical stain ing results, three of the tumors could possibly be reclassified: one a s a melanoma, one as a probable fibrosarcoma, and one as unknown. Thes e results also indicate that feline malignant fibrous histiocytomas sh ow a diversity of intermediate filament expression, as do human tumors . Our results also do not support the theory that malignant fibrous hi stiocytomas are of histiocytic origin.