Granular cell tumor of the breast.

Granular cell tumors (GCT) are uncommon, usually benign, neoplasms that are thought to derive from Schwann cells of the peripheral nerves. They can originate anywhere in the body but are most frequently found in the head and neck, particularly in the oral cavity. When they are located in the breast, as may occur in 5-8 per cent of cases, the clinical and pathologic appearance is similar to that of a malignant tumor. Immunohistochemical analysis, including reactivity for periodic acid-Schiff, CD68, and S100 and negative reactivity for cytokeratin, is required for definitive diagnosis. Awareness of this tumor's unique characteristics might aid in differentiating it from the more common malignant tumors of the breast.