MEN1 tumors (e.g., parathyroids, insulinoma, and lipoma) that do not have LOH have been shown to harbor different somatic and germ-line mutations of the MEN1 gene (Fig. 4) (Pannett and Thakker, 2001), and this is consistent with the Knudson two-hit hypothesis (Knudson et al., 1973). The gene discussed is MEN1; the disease is pancreatic insulinoma.