Carcinoid tumor

Carcinoid tumors are a type of neuroendocrine tumor that can occur in a number of locations. Carcinoid tumors arise from endocrine amine precursor uptake and decarboxylation (APUD) cells that can be found throughout the gastrointestinal tract as well as other organs (e.g. lung). In general, they are slow growing tumors but are nevertheless capable of metastasizing.

Clinical presentation

• can be variable, dependent on the location:
  • carcinoid tumors involving the jejunum and ileum can be large at presentation but are usually found incidentally
  • rectal carcinoids may cause pain
  • gastrointestinal tract carcinoid can present as vague abdominal pain
• carcinoid syndrome: in 8% of patients with a carcinoid tumor ⁹

Pathology

Location

• gastrointestinal tract carcinoid (60-85% of all carcinoids) ^11,12
  • small bowel: ~40% of gastrointestinal carcinoids, mostly in the terminal ileum
  • rectum (~22.5%)
  • colon (~15%)
  • appendix (~10%)
  • stomach (~7.5%)
  • pancreas (~7.5%)
• carcinoid tumors of the lung (~25% of all carcinoids)
  • bronchial carcinoid
  • peripheral pulmonary carcinoid tumors
• primary hepatic carcinoid
• ovarian carcinoid: accounts for 0.5% of carcinoid tumors and 0.3% of ovarian tumors ⁷
• thymic carcinoid

Markers

• 5-HIAA (5-hydroxyindoleacetic acid): usually suggests a functioning carcinoid tumor
• chromogranin A (CgA): considered a valuable tool in the diagnosis of neuroendocrine neoplasia in general ⁶

Radiographic features

CT/MRI

Refer to specific articles (above) for imaging characteristics.

Scintigraphy

¹¹¹In-octreotide (Octreoscan) will concentrate in gastrointestinal tract carcinoid tumors as well as in liver metastases, and is generally considered the test of choice due to its high sensitivity ¹⁴. 

¹²³I-MIBG will also concentrate in carcinoid tumors, including the low percentage (~15%) that are negative with ¹¹¹In-octreotide ¹³. 

⁶⁸Ga-octreotide PET scan: usually avid.

Treatment and prognosis

Complications

• cardiac valve lesions from carcinoid

History and etymology

It was initially coined by Oberndorfer in 1907 as “Karzinoide” to denote its resemblance to carcinoma ⁴.