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Locations and Classifications

Carcinoid Locations and Classification

Carcinoid tumors can develop almost anywhere in the body.  Carcinoid tumors can be classified by location, histology and biological activity in the following way:

Embryonic Gut Derivation

  • Foregut carcinoid tumors are located in the lungs, thymus, stomach, first part of the duodenum (small intestine) or the pancreas.
    • Gastric carcinoids (carcinoids of the stomach) are further classified as:
      • Type 1 - associated with chronic atrophic gastritis (inflammation of the stomach lining) caused by hypergastrinemia (high levels of the hormone gastrin).
      • Type 2 - implicated with Zollinger Ellison Syndrome and Multiple Endocrine Neoplasia Type 1 (MEN-1).
      • Type 3 - sporadic, not associated with hypergastrinemia, can cause Atypical Carcinoid S yndrome and are frequently malignant.
    • Pulmonary carcinoids (carcinoids in the lungs) are further classified as:
      • Typical pulmonary carcinoids (benign or low-grade malignant) - considered to be well-differentiated, commonly located in the center of the lungs, and rarely metastasize (Fink, Krelbaum, Yellin, Bendayan, Saute, Glazer, & Kramer, 2001; Kulke 2007).
      • Atypical pulmonary carcinoids (low-grade malignant) - poorly differentiated, commonly located in the periphery of lungs, characterized by frequent mitoses (cellular division), and frequently metastasize (Kulke, 2007; Fink et al., 2001).
  • Midgut carcinoid tumors are located in the small intestine, appendix, or right colon (large intestine).
  • Hindgut carcinoid tumors are located in the transverse colon, sigmoid colon, or rectum.

Presence of Clinical Syndrome

Functioning: A functioning carcinoid tumor secretes biochemically active substances such as hormones, which cause specific clinical syndromes such as Carcinoid Syndrome or Zollinger -Ellison syndrome

Non-functioning: A non-functioning carcinoid tumor secretes specific substances but these substances are either inactive and/or do not cause any clinical syndrome.

Inherited versus Sporadic

  • Sporadic: Cancer causing mutations arise randomly
  • Inherited: Cancer causing mutations are inherited due to MEN-1 or other familial factors

Carcinoid tumors can be familial or sporadic. Inherited carcinoid cancer refers to carcinoid cancer which is genetically inherited whereas sporadic carcinoid cancer has no hereditary basis. Carcinoid tumors are generally thought to be sporadic, except for a small proportion of which occur as a part of MEN (multiple endocrine neoplasia) syndromes (Babovic-Vuksanovic, Constantinou, Rubin, Rowland, Schaid, & Karnes, 1999). Other familial factors contribute to a small proportion of carcinoid tumors; these are less understood than MEN-1 causes.

Histological Features

Since neuroendocrine tumors, such as carcinoid cancer, represent a heterogeneous group of tumors, in 2000, the World Health Organization updated the classification system for them based upon their clinical pathological criteria (Kloppel, Perren, & Heitz, 2004). Each category includes both functioning and non-functioning tumors.

  • Well-differentiated endocrine tumors, with benign or uncertain behavior.
  • Well-differentiated endocrine carcinomas, with low-grade malignant behavior.
  • Poorly differentiated endocrine carcinomas, with high-grade malignant behavior.
  • Endocrine/exocrine carcinomas, with characteristics of both endocrine and exocrine tumors.

Carcinoid tumors and pancreatic neuroendocrine tumors generally fall within the classification of well-differentiated endocrine tumors. 


Babovic-Vuksanovic, D., Constantinous, C., Rubin, J., Rowland, C., Schiad, D., Karnes, P. (1999) Familial Occurrence of Carcinoid Tumors and Association with Other Malignant Neoplasms. Cancer Epidemiology, Biomarkers, & Prevention, 8, 715-719. Retrieved from:

Fink, G., Krelbaum, T., Yellin, A., Bendayan, D., Saute, M., Glazer, M., and Kramer, M. R. (2001). Pulmonary Carcinoid: Presentation, Diagnosis and Outcome in 142 Cases in Israel and Review of 640 Cases From the Literature. American College of Chest Physicians, 119(6), 1647-1651. Retrieved from:

Hemminki, J. and Li, X. (2001). Familial carcinoid tumors and subsequent cancers: a nation-wide epidemiologic study from Sweden. International Journal of Cancer, 94(3), 444-448. Retrieved from:

Kloppel, G., Perren, A., and Heitz, P. U. (2004). The gasteroenteropancreatic neuroendocrine cell system and its tumors: the WHO classification. Annals of the New York Academy of Science, 1014, 13-27. Retrieved from:

Kulke, M. H., (2007). Gastrointestinal neuroendocrine tumors: a role for targeted therapies? Endocrine Related Cancer, 14(2), 207-219. Retrieved from:

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