Amyloid formation in insulinoma.

Local amyloid depositions were investigated with electron microscopy in a functioning beta cell adenoma of the pancreas. Beta granule-containing neoplastic cells adjoining small amyloid depositions were shown to have cellular invaginations containing radiating amyloid bundles, indicating the neoplastic cells were involved in the formation of amyloid. Seen in the larger mayloid depositions were attenuated, thin, cellular processes of the neoplastic cells, separating the amyloid stroma into globules. The globular separations of the amyloid correlated well with the light-microscopic globular appearance of amyloid stroma. Possible mechanisms are discussed for the amyloid deposition of insulinoma with relation to amyloidogenesis of other types of amyloidosis.