Intestinal carcinoid tumors are well-differentiated neuroendocrine tumors, which arise from glandular endocrine cells called enterochromaffin cells. Patients affected with this condition show symptoms of cramping intestinal pain, obstruction in the bowel movement, nausea, vomiting, diarrhea, and malnutrition due to malabsorption of nutrients. Most of these symptoms are due to obstruction of the bowel by the tumor, either due to the growth of the tumor into the intestinal lumen, or due to fibrosing mesenteritis causing small intestinal kinking and gangrene. Some of the patients, however, go on to develop carcinoid syndrome, caused by the excess production of hormone by the tumors. Carcinoid syndrome is characterized by hot flushes of the head and neck, and cyanosis. About one in every 300 individuals is said to be affected by intestinal carcinoid tumors. However, in the majority of these patients, the tumors are too small to cause any untoward effect, and remain undetected. This is one of the reasons for the late detection of these tumors, and for its spread to local tissues and lymph nodes.
Carcinoid tumors can be detected in a variety of ways. Assaying the amount of urinary 5-hydroxy indole acetic acid is one of the major methods. Other diagnostic tests include CT, MRI, arteriography, and radionuclide scanning. Biopsies of the tumors can also confirm the diagnosis, as the enterochromaffin cells stain in a peculiar way. If tumors cause obstruction in the intestine, they need to be surgically removed. Destroying the tumor also reduces the hormonal effect exerted by them. The most effective type of chemotherapy involves combination therapy with several anti cancer drugs. On the whole, the survival rate of patients affected with carcinoid tumors is good, with survival up to 23 years being noted.
The tumor suppressor gene, SDHD (Succinate-Ubiquinone Oxidoreductase Subunit D) has been found to be responsible for the development of intestinal carcinoid tumors. Heterozygous sequence variants of the SDHD gene were detected in at least a small number of patients. Characterized mutations in the SDHD gene, known to lead to development of intestinal carcinoids include H50R and G12S.