Summary:The histogenesis of granular cell tumor (GCT) has been a source of controversy since its recognition as an entity by Abrikossoff in 1926. These lesions can occur in virtually any location. Benign GCTs are not uncommon, but malignant ones are rare and at times difficult to diagnose. The main morphologic feature is the granularity of the cytoplasm which is caused by a massive accumulation of lysosomes. Early suggestions that GCT may have a myoblastic origin have been discounted and use of the term granular cell myoblastoma as a designation for this tumor is discouraged. Although most investigators currently favor a Schwann cell derivation based on immunohistochemical and electron microscopic findings and advocate the designation of granular cell schwannoma, some differences exist between schwannomas and GCTs in their ultrastructural characteristics and the expression of some immunohistochemical markers. Other investigators believe that GCT is not a specific entity but rather a degenerative change that can occur not only in Schwann cells but also in a variety of other normal and neoplastic cells. Until more information becomes available, particularly that derived from cytogenetic studies, this lesion should be considered a separate entity and the descriptive designation of granular cell tumor continues to be appropriate.