Feline peripheral nerve sheath tumors: histologic, immunohistochemical, and clinicopathologic correlation (59 tumors in 53 cats).

Feline peripheral nerve sheath tumors are uncommonly reported, and their clinical behavior has not been well documented. Fifty-nine peripheral nerve sheath tumors were collected from 53 cats. All of the tumors involved skin, subcutis, skeletal muscle, and/or mucous membranes. Histologically, the tumors were composed of compact to loosely arranged streams and fascicles of spindled cells with eosinophilic, often wavy cytoplasmic processes; small to occasionally moderate amounts of collagenous to myxoid matrix; and nuclear palisading. Immunohistochemically, all tumors were positive for vimentin and S-100 protein, 44 of 59 were positive for glial fibrillary acidic protein (GFAP), and all were negative for muscle specific actin. The tumors fell into 3 histologic categories: 34 benign tumors with Antoni A areas that were S-100 protein and GFAP positive, 9 benign tumors that lacked Antoni A areas and were S-100 protein positive and GFAP negative, and 16 tumors with features of malignancy. Seventy-five percent of these cases involved the head, neck, or limbs. Recurrent tumors were submitted or tumors were reported to have recurred in 9 cases. Tumor recurrence was reported for all 3 of the histologic subtypes. None was documented as having metastasized.