An unusual benign or malignant neoplasm characterized by the presence of neoplastic large polygonal cells with granular, eosinophilic cytoplasm which contains abundant lysosomes. It was originally thought to be a tumor originating from muscle cells and was named granular cell myoblastoma. Subsequent studies have suggested a derivation from Schwann cells. It affects females more often than males and it usually presents as a solitary mass. A minority of patients have multiple tumors. It can arise from many anatomic sites including the posterior pituitary gland, skin, oral cavity, esophagus, stomach, heart, mediastinum, and breast. [from
NCI]