Multiple visceral and cutaneous granular cell tumors. Ultrastructural and immunocytochemical evidence of Schwann cell origin.

Granular cell tumor of the stomach is rare and may occur in association with similar tumors in the skin. Two such tumors were found in association with cutaneous granular cell tumors in two black females. Infiltrating carcinoma of the stomach was suspected at surgery in one case. All of the lesions were typical granular cell tumors on light microscopic examination. Ultrastructural examination showed clusters of tumor cells that were surrounded by basal laminae and axonal structures were present among the tumor cells. S-100 protein immunoreactivity was also demonstrated in the tumor cells. These findings suggest a Schwannian origin for visceral granular cell tumors.