Intestinal neuroendocrine tumors (NETs) constitute a heterogeneous group with duodenal, small intestinal, colonic and rectal NETs. They constitute more than half of all NETs, with the highest frequencies in the rectum, small intestine, and colon. The tumor biology varies with the location of the primary tumor as well as with the grade and staging of the tumor. Small intestinal NETs usually present low proliferation and are treated in the first line with somatostatin analogs according to current guidelines. If progression occurs, one can add interferon alpha or change the treatment to everolimus. Peptide receptor radionuclide therapy (PRRT) with Lutetium177-DOTATATE can be an option in the future after registration of the compound. Rectal tumors are usually small when they metastasize; they can be treated with somatostatin analogs but more so with PRRT, while another option is of course everolimus. Colonic NETs are more aggressive than the rest of intestinal NETs and will be treated with everolimus, sometimes in combination with somatostatin analogs based on positive scintigraphy. Another option is a cytotoxic agent such as streptozotocin plus 5-fluorouracil (5-FU) or temozolomide plus capecitabine. The most aggressive tumors, i.e. neuroendocrine carcinoma G3, are treated with a platin-based therapy plus etoposide; if they present with a lower proliferation, i.e. <50%, temozolomide plus capecitabine plus bevacizumab can also be attempted. Duodenal NETs are mostly treated similar to pancreatic NETs, either with cytotoxic agents, streptozotocin plus 5-FU, or temozolomide plus capecitabine, or with targeted agents such as everolimus.

1.
Lawrence B, Gustafsson BI, Chan A, Svejda B, Kidd M, Modlin IM: The epidemiology of gastroenteropancreatic neuroendocrine tumors. Endocrinol Metab Clin North Am 2011;40:1-18, vii.
2.
Tang LH, Untch BR, Reidy DL, O'Reilly E, Dhall D, Jih L, Basturk O, Allen PJ, Klimstra DS: Well-differentiated neuroendocrine tumors with a morphologically apparent high-grade component: a pathway distinct from poorly differentiated neuroendocrine carcinomas. Clin Cancer Res 2016;22:1011-1017.
3.
Klöppel G, Rindi G, Perren A, Komminoth P, Klimstra DS: The ENETS and AJCC/UICC TNM classifications of the neuroendocrine tumors of the gastrointestinal tract and the pancreas: a statement. Virchows Arch 2010;456:595-597.
4.
Klöppel G: Classification and pathology of gastroenteropancreatic neuroendocrine neoplasms. Endocr Relat Cancer 2011;18(suppl 1):S1-16.
5.
Banck MS, Kanwar R, Kulkarni AA, et al: The genomic landscape of small intestine neuroendocrine tumors. J Clin Invest 2013;123:2502-2508.
6.
Francis JM, Kiezun A, Ramos AH, et al: Somatic mutation of CDKN1B in small intestine neuroendocrine tumors. Nat Genet 2013;45:1483-1486.
7.
Tang LH, Contractor T, Clausen R, Klimstra DS, Du YC, Allen PJ, Brennan MF, Levine AJ, Harris CR: Attenuation of the retinoblastoma pathway in pancreatic neuroendocrine tumors due to increased cdk4/cdk6. Clin Cancer Res 2012;18:4612-4620.
8.
La Rosa S, Marando A, Furlan D, Sahnane N, Capella C: Colorectal poorly differentiated neuroendocrine carcinomas and mixed adenoneuroendocrine carcinomas: insights into the diagnostic immunophenotype, assessment of methylation profile, and search for prognostic markers. Am J Surg Pathol 2012;36:601-611.
9.
Stricker I, Tzivras D, Nambiar S, Wulf J, Liffers ST, Vogt M, Verdoodt B, Tannapfel A, Mirmohammadsadegh A: Site- and grade-specific diversity of LINE1 methylation pattern in gastroenteropancreatic neuroendocrine tumours. Anticancer Res 2012;32:3699-3706.
10.
Dammann R, Schagdarsurengin U, Strunnikova M, Rastetter M, Seidel C, Liu L, Tommasi S, Pfeifer GP: Epigenetic inactivation of the Ras-association domain family 1 (RASSF1A) gene and its function in human carcinogenesis. Histol Histopathol 2003;18:665-677.
11.
Reubi JC: Peptide receptors as molecular targets for cancer diagnosis and therapy. Endocr Rev 2003;24:389-427.
12.
Reubi JC, Waser B: Concomitant expression of several peptide receptors in neuroendocrine tumours: molecular basis for in vivo multireceptor tumour targeting. Eur J Nucl Med Mol Imaging 2003;30:781-793.
13.
Strosberg J: Neuroendocrine tumours of the small intestine. Best Pract Res Clin Gastroenterol 2012;26:755-773.
14.
Ahmed A, Turner G, King B, et al: Midgut neuroendocrine tumours with liver metastases: results of the UKINETS study. Endocr Relat Cancer 2009;16:885-894.
15.
Öberg K, Kvols L, Caplin M, Delle Fave G, De Herder W, Rindi G, Ruszniewski P, Woltering EA, Wiedenmann B: Consensus report on the use of somatostatin analogs for the management of neuroendocrine tumors of the gastroenteropancreatic system. Ann Oncol 2004;15:966-973.
16.
Eriksson B, Öberg K: Summing up 15 years of somatostatin analog therapy in neuroendocrine tumors: future outlook. Ann Oncol 1999;10(suppl 2):S31-38.
17.
Kvols LK, Moertel CG, O'Connell MJ, Schutt AJ, Rubin J, Hahn RG: Treatment of the malignant carcinoid syndrome. Evaluation of a long-acting somatostatin analogue. N Engl J Med 1986;315:663-666.
18.
Rinke A, Muller HH, Schade-Brittinger C, et al: Placebo-controlled, double-blind, prospective, randomized study on the effect of octreotide LAR in the control of tumor growth in patients with metastatic neuroendocrine midgut tumors: a report from the PROMID Study Group. J Clin Oncol 2009;27:4656-4663.
19.
Caplin ME, Pavel M, Cwikla JB, et al.; CLARINET Investigators: Lanreotide in metastatic enteropancreatic neuroendocrine tumors. N Engl J Med 2014;371:224-233.
20.
Pavel M, O'Toole D, Costa F, et al: ENETS Consensus Guidelines update for the management of distant metastatic disease of intestinal, pancreatic, bronchial neuroendocrine neoplasms (NEN) and NEN of unknown primary site. Neuroendocrinology 2016;103:172-185.
21.
Bauer W, Briner U, Doepfner W, Haller R, Huguenin R, Marbach P, Petcher TJ, Pless: SMS 201-995: a very potent and selective octapeptide analogue of somatostatin with prolonged action. Life Sci 1982;31:1133-1140.
22.
Lancranjan I, Bruns C, Grass P, et al: Sandostatin LAR: a promising therapeutic tool in the management of acromegalic patients. Metabolism 1996;45(suppl 1):67-71.
23.
Martín-Richard M, Massuté B, Pineda E, et al: Antiproliferative effects of lanreotide autogel in patients with progressive, well-differentiated neuroendocrine tumours: a Spanish, multicentre, open-label, single arm phase II study. BMC Cancer 2013;13:427.
24.
Sideris L, Dube P, Rinke A: Antitumor effects of somatostatin analogs in neuroendocrine tumors. Oncologist 2012;17:747-755.
25.
Trendle MC, Moertel CG, Kvols LK: Incidence and morbidity of cholelithiasis in patients receiving chronic octreotide for metastatic carcinoid and malignant islet cell tumors. Cancer 1997;79:830-834.
26.
Kvols LK, Öberg KE, O'Dorisio TM, et al: Pasireotide (SOM230) shows efficacy and tolerability in the treatment of patients with advanced neuroendocrine tumors refractory or resistant to octreotide LAR: results from a phase II study. Endocr Relat Cancer 2012;19:657-666.
27.
Wolin EM, Jarzab B, Eriksson B, et al: Phase III study of pasireotide long-acting release in patients with metastatic neuroendocrine tumors and carcinoid symptoms refractory to available somatostatin analogues. Drug Des Devel Ther 2015;9:5075-5086.
28.
Strosberg J, El-Haddad G, Wolin E, et al: Phase 3 trial of 177Lu-Dotatate for midgut neuroendocrine tumors. N Engl J Med 2017;376:125-135.
29.
Eriksson B, Klöppel G, Krenning E, et al: Consensus guidelines for the management of patients with digestive neuroendocrine tumors - well-differentiated jejunal-ileal tumor/carcinoma. Neuroendocrinology 2008;87:8-19.
30.
Öberg K: Interferon-alpha versus somatostatin or the combination of both in gastro-enteropancreatic tumours. Digestion 1996;57(suppl 1):81-83.
31.
Pavel ME, Baum U, Hahn EG, Schuppan D, Lohmann T: Efficacy and tolerability of pegylated IFN-alpha in patients with neuroendocrine gastroenteropancreatic carcinomas. J Interferon Cytokine Res 2006;26:8-13.
32.
Yao JC, Guthrie KA, Moran C, et al: Phase III prospective randomized comparison trial of depot octreotide plus interferon alfa-2b versus depot octreotide plus bevacizumab in patients with advanced carcinoid tumors: SWOG S0518. J Clin Oncol 2017;35:1695-1703.
33.
Yao JC, Fazio N, Singh S, et al: Everolimus for the treatment of advanced, non-functional neuroendocrine tumours of the lung or gastrointestinal tract (RADIANT-4): a randomised, placebo-controlled, phase 3 study. Lancet 2016;387:968-977.
34.
Pavel ME, Hainsworth JD, Baudin E, et al: Everolimus plus octreotide long-acting repeatable for the treatment of advanced neuroendocrine tumours associated with carcinoid syndrome (RADIANT-2): a randomised, placebo-controlled, phase 3 study. Lancet 2011;378:2005-2012.
35.
Lamarca A, Barriuso J, McNamara MG, Hubner RA, Valle JW: Telotristat ethyl: a new option for the management of carcinoid syndrome. Expert Opin Pharmacother 2016;17:2487-2498.
36.
Modlin IM, Öberg K, Chung DC, et al: Gastroenteropancreatic neuroendocrine tumours. Lancet Oncol 2008;9:61-72.
37.
Mandair D, Caplin ME: Colonic and rectal NET's. Best Pract Res 2012;26:775-789.
38.
Caplin M, Sundin A, Nillson O, Baum RP, Klose KJ, Kelestimur F, Plockinger U, Papotti M, Salazar R, Pascher A: ENETS Consensus Guidelines for the management of patients with digestive neuroendocrine neoplasms: colorectal neuroendocrine neoplasms. Neuroendocrinology 2012;95:88-97.
39.
Niederle MB, Hackl M, Kaserer K, Niederle B: Gastroenteropancreatic neuroendocrine tumours: the current incidence and staging based on the WHO and European Neuroendocrine Tumour Society classification: an analysis based on prospectively collected parameters. Endocr Relat Cancer 2010;17:909-918.
40.
Sorbye H, Welin S, Langer SW, et al: Predictive and prognostic factors for treatment and survival in 305 patients with advanced gastrointestinal neuroendocrine carcinoma (WHO G3): the NORDIC NEC study. Ann Oncol 2013;24:152-160.
41.
Yamaguchi T, Machida N, Morizane C, et al: Multicenter retrospective analysis of systemic chemotherapy for advanced neuroendocrine carcinoma of the digestive system. Cancer Sci 2014;105:1176-1181.
42.
Welin S, Sorbye H, Sebjornsen S, Knappskog S, Busch C, Öberg K: Clinical effect of temozolomide-based chemotherapy in poorly differentiated endocrine carcinoma after progression on first-line chemotherapy. Cancer 2011;117:4617-4622.
43.
O'Connor JM, Marmissolle F, Bestani C, et al: Observational study of patients with gastroenteropancreatic and bronchial neuroendocrine tumors in Argentina: results from the large database of a multidisciplinary group clinical multicenter study. Mol Clin Oncol 2014;2:673-684.
44.
Yao JC, Hassan M, Phan A, et al: One hundred years after ‘carcinoid': epidemiology of and prognostic factors for neuroendocrine tumors in 35,825 cases in the United States. J Clin Oncol 2008;26:3063-3072.
45.
Modlin IM, Lye KD, Kidd M: A 50-year analysis of 562 gastric carcinoids: small tumor or larger problem? Am J Gastroenterol 2004;99:23-32.
46.
Mullen JT, Wang H, Yao JC, Lee JH, Perrier ND, Pisters PW, Lee JE, Evans DB: Carcinoid tumors of the duodenum. Surgery 2005;138:971-977; discussion 977-978.
47.
Kölby L, Nilsson O, Ahlman H: Gastroduodenal endocrine tumours. Scand J Surg 2004;93:317-323.
48.
Rindi G, Bordi C, Rappel S, La Rosa S, Stolte M, Solcia E: Gastric carcinoids and neuroendocrine carcinomas: pathogenesis, pathology, and behavior. World J Surg 1996;20:168-172.
49.
La Rosa S, Inzani F, Vanoli A, Klersy C, Dainese L, Rindi G, Capella C, Bordi C, Solcia E: Histologic characterization and improved prognostic evaluation of 209 gastric neuroendocrine neoplasms. Hum Pathol 2011;42:1373-1384.
50.
Rindi G, Azzoni C, La Rosa S, Klersy C, Paolotti D, Rappel S, Stolte M, Capella C, Bordi C, Solcia E: ECL cell tumor and poorly differentiated endocrine carcinoma of the stomach: prognostic evaluation by pathological analysis. Gastroenterology 1999;116:532-542.
51.
Jianu CS, Fossmark R, Syversen U, Hauso O, Fykse V, Waldum HL: Five-year follow-up of patients treated for 1 year with octreotide long-acting release for enterochromaffin-like cell carcinoids. Scand J Gastroenterol 2011;46:456-463.
52.
Fossmark R, Sordal O, Jianu CS, Qvigstad G, Nordrum IS, Boyce M, Waldum HL: Treatment of gastric carcinoids type 1 with the gastrin receptor antagonist netazepide (YF476) results in regression of tumours and normalisation of serum chromogranin A. Aliment Pharmacol Ther 2012;36:1067-1075.
53.
Moore AR, Boyce M, Steele IA, Campbell F, Varro A, Pritchard DM: Netazepide, a gastrin receptor antagonist, normalises tumour biomarkers and causes regression of type 1 gastric neuroendocrine tumours in a nonrandomised trial of patients with chronic atrophic gastritis. PloS One 2013;8:e76462.
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