Granular cell tumor. Immunohistochemical analysis of 21 benign tumors and one malignant tumor.

We examined the immunohistochemical profile of 21 granular cell tumors (GCTs) and a single clinically malignant GCT using a panel of commercially available antibodies. All cases showed diffuse cytoplasmic and nuclear staining for S100 protein. Fourteen cases stained for myelin basic protein, Leu-7, or both. Immunostains for neurofilament protein and glial fibrillary acidic protein were negative in all cases. Stains for cathepsin B and alpha 1-antichymotrypsin were positive in 21 and 15 cases, respectively. Cathepsin-B reactivity may reflect autodigestion of myelin, while the presence of alpha 1-antichymotrypsin is less specific and may be related to cellular production of this product or to nonspecific uptake of alpha 1-antichymotrypsin in serum during the formation of phagolysosomes. All tumors expressed vimentin, often in a distinctive peripheral cytoplasmic pattern. Focal desmin staining was seen in three separate specimens from the patients with the malignant GCT, but this tumor also expressed S100 protein, myelin basic protein, and Leu-7 and did not stain for muscle-specific actin. The desmin reactivity in this single case probably represents non-specific staining rather than myogenous differentiation, since the reactivity to other nerve sheath markers shows histogenetic similarity with the benign GCTs. These findings support a Schwann cell origin for nongingival GCTs and illustrate a useful panel of commercially available antibodies to diagnose these distinctive tumors.