Carcinoid tumour and carcinoid syndrome

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What is Carcinoid tumour and carcinoid syndrome?

Carcinoid tumour is a type of neuroendocrine tumour. Neuroendocrine tumours are tumours of the neuroendocrine cells that secrete regulatory hormones and are present in the nervous and endocrine/hormonal system.

Most primary carcinoid tumours arise from enterochromaffin cells of the gastrointestinal/digestive tract, with the most common sites being the appendix, small bowel and rectum. They can also be seen in the liver, pancreas, bronchus (branch of the windpipe into the lung), and ovaries.

Carcinoid tumours can be classified based on the primitive gut that gives rise to the tumour (ie, foregut, midgut, hindgut). Examples of foregut carcinoid tumours are carcinoids of the bronchus, stomach, beginning portion of the small bowel (proximal part of duodenum) and pancreas. Midgut tumours are derived from the rest of the small bowel (second portion of duodenum, jejunum, ileum), and part of the large bowel (right colon). These are the most common type of carcinoid tumours in adults. Hindgut carcinoid tumors include those of the large bowel (transverse colon, descending colon, and rectum).

Carcinoid tumours produce, store, and release a variety of hormones and other substances (polypeptides, biogenic amines, and prostaglandins). Amines produced include serotonin, 5-hydroxytryptophan, norepinephrine, histamine and dopamine. Examples of polypeptides produced are kallikrein, bradykynin, somatostatin, neuropeptide K, neurokinin A, ACTH, growth hormone, glucagon etc.

Carcinoid syndrome is the term applied to a group of symptoms mediated by various substances produced by some carcinoid tumours. Symptoms commonly experienced in carcinoid syndrome are flushing, diarrhoea and cramping. Heart failure due to valve problems may also occur.

The main biologically active peptides secreted in carcinoid syndrome are serotonin and possibly tachykinins, motilin, prostaglandins. In intestinal carcinoid tumours, the occurrence of carcinoid syndrome usually implies liver involvement.

Who gets Carcinoid tumour and carcinoid syndrome?

Carcinoid tumours are rare. In the United States, there were about 13,000 cases identified from 1950 to 1999. The estimated occurrence rate is 2.0/100,000 for men and 2.4/100,000 for women. The tumour is most common among African males.

The age range at which the tumour occurs is between the second and the ninth decade.

About 67% of cases occur in the digestive tract while another 25% occur in the airway and lungs.

Carcinoid syndrome is relatively rare. The number of new cases per year is 0.5-2.0 per 1,000,000 population. It occurs in approximately 10% of patients with small bowel carcinoid tumour. Less than 1% of carcinoid tumours in the appendix are associated with carcinoid syndrome. Among patients with carcinoid syndrome, a large proportion (75-80%) has small bowel carcinoids.

Predisposing Factors

The cause if virtually unknown.

Factors that are associated with an increased occurrence of carcinoid tumour are:

a family history of carcinoid in a first-degree relative (3.6 times the risk)

a well-educated social background (2.8 times the risk)

birth in a large city (1.39 times the risk)

Genetic influences are suspected. Reported genetic abnormalities include changes in the chromosome.

Progression

When carcinoid tumours happen alone (without carcinoid syndrome), diagnosis is often delayed due to the vagueness of symptoms. Carcinoids in the duodenum (first part of small bowel), stomach and rectum are most frequently found by chance at endoscopy (a procedure involving passing a tube with a camera through the mouth or the bottom end to look at the digestive tract). Those in the appendix are almost always found incidentally during surgery.

Carcinoid tumours are slow-growing. About one in nine patients with carcinoid have distant spread to other organs (metastasis) when carcinoid tumour is diagnosed.

Metastasis at diagnosis is most common in small bowel and large bowel carcinoids, whereas carcinoids in the rectum, airway and stomach are less likely to spread.

In the majority (about 90%) of cases, carcinoid syndrome occurs after distant spread to the liver. There are, however, exceptions, for example carcinoids in the airway or ovaries, where carcinoid syndrome can rarely happen without liver involvement.

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