Overview of Carcinoids
Carcinoid tumors, or carcinoids, originate in hormone-producing cells of the gastrointestinal (GI) tract (i.e., esophagus, stomach, small intestine, colon), the respiratory tract (i.e., lungs, trachea, bronchi), the hepatobiliary system (i.e., pancreas, gallbladder, liver), and the reproductive glands (i.e., testes, ovaries).
The most common site of origin is the GI tract and carcinoid tumors often develop in the appendix, the rectum, and the lower sections of the small intestine (i.e., the jejunum and the ileum). The large tubes that lead from the windpipe to the lungs (bronchi) are other common sites of origin.
Carcinoids are classified as neuroendocrine tumors. They develop in peptide- and amine-producing cells, which release hormones in response to signals from the nervous system. Excessive amounts of these hormones cause a condition called carcinoid syndrome in approximately 10 percent of patients with carcinoid tumors.
Carcinoids are slow growing and tumors with the same site of origin often have different characteristics and growth patterns. They can be subdivided according to the following:
- Cellular growth pattern (e.g., trabecular, glandular, undifferentiated, mixed)
- Hormones produced (e.g., bradykinin, serotonin, histamine, prostaglandins)
- Site of origin – foregut (respiratory tract, pancreas, stomach, first section of the small intestine [duodenum]), midgut (jejunum, ileum, appendix, diverticulum, ascending colon), or hindgut (transverse colon, descending colon, rectum)
Incidence & Prevalence of Carcinoid Tumors
According to the American Cancer Society, approximately 5,000 carcinoid tumors are diagnosed each year in the United States. According to the National Cancer Institute (NCI), approximately 74 percent of these tumors originate in the GI tract (e.g., intestines) and 25 percent occur in the respiratory tract (e.g., lungs).
Carcinoids are rare in children and are more common in patients older than the age of 50. They are twice as common in men. Carcinoid tumors of the appendix usually are benign and often occur between the ages of 20 and 40.