Comparison of genetic alterations in neuroendocrine tumors: frequent loss of chromosome 18 in ileal carcinoid tumors.

Carcinoid tumors and pancreatic endocrine tumors are uncommon neuroendocrine neoplasms, and their genetic alterations are not well characterized. These tumors have site-specific differences in neuroendocrine characteristics, clinical course and genetic alterations. We compared clinicopathological features and loss of heterozygosity of chromosomes 11q, 16q and 18, and BRAF gene mutations in 47 patients with neuroendocrine tumors including 16 with pancreatic endocrine tumors, 15 with nonileal carcinoid tumors and 16 with ileal carcinoid tumors. Patients with carcinoid tumors had more frequent history of alcohol consumption compared to patients with pancreatic endocrine tumors (P=0.02), and patients with ileal carcinoid tumors more frequently had liver metastasis compared to patients with nonileal carcinoid tumors and pancreatic endocrine tumors (P=0.02). Allelic loss of chromosome 11q was present in 21% of tumors, chromosome 16q in 13%, and chromosome 18 in 30%. These alterations differed with the anatomical subsite of tumor: allelic loss of chromosome 18 was present in 69% of ileal carcinoid tumors, 13% of nonileal carcinoid tumors and 6% of pancreatic endocrine tumors (P=0.001). In contrast to pancreatic endocrine tumors and nonileal carcinoid tumors, all 11 ileal tumors with loss of chromosome 18 had complete loss of both chromosomal arms. No BRAF mutations were identified. Complete allelic loss of chromosome 18 was associated with smaller tumor size (P=0.02). Our study indicates that genetic alterations vary by tumor subsite and clinicopathologic features, and ileal carcinoid tumors have distinctive clinicopathologic and genetic profiles.