Immunohistochemical localization of autophagosomal membrane-associated protein LC3 in granular cell tumor and schwannoma

Granular cell tumor (GCT) is a neoplasm derived from Schwann cell or (in cases arising in the neurohypophysis) pituicyte and is characterized by abundant cytoplasm filled with numerous eosinophilic granules, which have been considered autophagolysosomes on the basis of their ultrastructure. To confirm that the formation of these granules is related to an autophagy phenomenon, 12 cases of GCT (including two cases of GCT of the neurohypophysis) were studied immunohistochemically using an antibody against LC3 (microtubule-associated protein 1 light chain 3, a specific marker of autophagy). All cases of GCT showed granular immunoreactivity for LC3 in the cytoplasm of tumor cells, indicating that the formation of intracytoplasmic granules in GCT is closely related to an autophagy phenomenon. For elucidation of the relationship between GCT and schwannoma, 20 cases of schwannoma were similarly studied using the anti-LC3 antibody. In eight of 20 cases, a small number of tumor cells showed granular immunoreactivity for LC3, suggesting an increased autophagic activity in some schwannomas and further reinforcing the close relationship between GCT and schwannoma.