Finally, the clinical applications provided by the understanding of the effects of MEN1 gene mutations on neuroendocrine tumor development in patients with this familial cancer syndrome are discussed.
MENIN expression was reduced in pancreatic vs. extrapancreatic NET (p = 0.008) and in insulinomas vs. nonfunctional GEP-NET (p = 0.019) and NET associated with the carcinoid syndrome (p = 0.029).
The MEN1 gene locus is known to be partly responsible for the tumorigenesis of sporadic gastric neuroendocrine tumors, but the genetic events that drive the neoplastic process of this tumor remain largely unknown.
Two novel mutations are identified in the MEN1 gene from nine archived paraffin-embedded neuroendocrine tumors, demonstrating that retrospective genetic analysis can be used to identify mutations in the MEN1 gene from preserved tissue.
In conclusion, LOH in the 11q13-14 regions is frequently found in type I carcinoids and neuroendocrine carcinomas of the stomach, suggesting the involvement of the MEN1 gene and/or a more telomeric tumor suppressor gene in the pathogenesis of these non-MEN-1-associated neuroendocrine tumors.
A germline mutation of the MEN1 gene was detected, and deletions of the MEN1 gene were consistently detected in multiple neuroendocrine tumors involving the parathyroid glands and the pancreas and a hepatic neuroendocrine tumor metastasis, as predicted by Knudson's "two hit" hypothesis.
Allelic deletion of the MEN1 locus was identified in 18/49 (36.7%) tumors (13/30, 43.3% in EPT and 5/19, 26.3% in NET) and mutations of the MEN1 gene were present in 8/52 (15.3%) tumors (4/30 (13.3%) EPT and 4/22 (18.1%) NET).
Although the number of MEN4 patients is low, the discovery of this syndrome has demonstrated a novel role for CDKN1B as a tumor susceptibility gene for neuroendocrine tumors.