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

Most carcinoid tumors histologically arise from enterochromaffine cells in Lieberkuhn crypts. They more often originate from the distal part of the ileum and produce serotonin ¹⁷.

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.

Nuclear medicine

• gallium-68 octreotide PET-CT (e.g. Ga-68 DOTATATE) has shown improved accuracy for detection of neuroendocrine tumors relative to indium-111 pentetreotide (Octreoscan) SPECT/CT ^13,14
• indium-111 octreotide (e.g. Octreoscan) SPECT-CT ¹⁵
• iodine-123 MIBG will also concentrate on carcinoid tumors, including the low percentage (~15%) that are negative with indium-111 octreotide ¹⁶

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.