Pancreatic islet tumors are relatively rare in the general population but occur frequently in patients with MEN 1. Delineation of the genetic events leading to neoplastic transformation of islet cells is at an early stage; but based on tumor deletion studies, it appears that inactivation of the MEN 1 gene is an early step in carcinogenesis for both sporadic and MEN 1-related tumors. Limited data also suggested a role for other tumor suppressors including the retinoblastoma, adenomatous polyposis coli, and Gorlin syndrome genes. Activation of oncogenes has not been identified in pancreatic islet tumors.