Carcinoid tumors are relatively uncommon neoplasms that nonetheless comprise up to 85% of neuroendocrine gastrointestinal neoplasms. They most frequently occur in the midgut and develop from neuroendocrine cells that are normally and diffusely present in this location. Most carcinoids are sporadic but epidemiological studies report a familial risk. Moreover, carcinoids can occur within the multiple endocrine neoplasia (MEN) syndrome, a rare familiar tumor syndrome in which mutations in the MEN1 gene are manifested. Recently, it has been shown that a majority (78%) of sporadic carcinoids display loss of heterozygosity for markers around the MEN 1 region, thus suggesting involvement of this gene in the pathogenesis of both familial and sporadic carcinoids.
