carcinoid n : a small tumor (benign or malignant) arising from the mucosa of the gastrointestinal tract; usually associated with excessive secretion of serotonin

Carcinoid (also carcinoid tumour or carcinoid tumor) is slow-growing but malignant type of neuroendocrine tumour, originating in the cells of the neuroendocrine system. Carcinoid tumours are apudomas that arise from the enterochromaffin cells throughout the gut. They are most commonly found in the foregut (35.6% cases) with lung, bronchus and trachea constituting 27.9% cases from where they rarely metastasise (except in case of pancreas). The next most common affected area is the small intestine especially the midgut (32.1% cases) with the highest proportion from ileum at 14.9% of all cases [as per the PAN-SEER data (1973-1999)]. In cases of metastases it can lead to carcinoid syndrome. This is due to the production of serotonin, which is released into the systemic circulation, which leads to symptoms of cutaneous flushing, diarrhea, bronchoconstriction and right-sided cardiac valve disease.

They were first characterized in 1907 by Siegfried Oberndorfer, a German pathologist at the University of Munich, who coined the term karzinoide, or "carcinoma-like", to describe the unique feature of behaving like a benign tumour despite having a malignant appearance microscopically. The recognition of their endocrine-related properties were later described by Gosset and Masson in 1914, and these tumours are now known to arise from the enterochromaffin (EC) and enterochromaffin-like (ECL) cells of the gut.

Symptoms

Most carcinoids are asymptomatic through the natural lifetime and are discovered only upon surgery for unrelated reasons; these are called coincidental carcinoids. But all carcinoids are considered to have malignant potential.

About 10 percent of carcinoids secrete excessive levels of a range of hormones, most notably serotonin (5-HT), causing:

• Flushing
• Diarrhea
• Wheezing
• Abdominal cramping
• Peripheral edema

This constellation of symptoms is called carcinoid syndrome or (if acute) carcinoid crisis. Occasionally, haemorrhage or the effects of tumour bulk are the presenting symptoms. The most common originating sites of carcinoid is the small bowel, particularly the ileum; carcinoid tumors are the most common malignancy of the appendix, and ovarian origin, though reported, is rare.

Treatment

Surgery, if feasible, is the only curative therapy. If the tumor has metastasized (most commonly, to the liver) and considered incurable. There are some promising treatment modalities, such as radiolabeled octreotide,, for arresting the growth of the tumors and prolonging survival in patients with liver metastases, though these are currently experimental.

Chemotherapy is of little benefit and is generally not indicated. Octreotide (a somatostatin analogue) may decrease the secretory activity of the carcinoid.

Carcinoid tumors are the most common malignant tumor of the appendix, but they are most commonly associated with the small intestine, and they can also be found in the rectum and stomach. They are known to grow in the liver, but this finding is usually a manifestation of metastatic disease from a primary carcinoid occurring elsewhere in the body. They have a very slow growth rate compared to most malignant tumors.

Goblet Cell Carcinoid

This is considered to be a hybrid between an exocrine and endocrine tumour derived from crypt cells of the appendix. Histologically, it forms clusters of goblet cells containing mucin with a minor admixture of Paneth cells and endocrine cells. The growth pattern is distinctive: typically producing a concentric band of tumour nests interspersed among the muscle and stroma of the appendiceal wall extending up the shaft of the appendix. This makes the lesion difficult to suspect grossly and difficult to measure. Small tumour nests may be camouflaged amongst the muscle or in periappendiceal fat; cytokeratin preparations best demonstrate the tumour cells; mucin stains are also helpful in identifying them. They behave in a more aggressive manner than do classical appendiceal carcinoids. Spread is usually to regional lymph nodes, peritoneum, and particularly the ovary. They do not produce sufficient hormonal substances to cause the carcinoid or other endocrine syndromes. In fact, they more closely resemble exocrine than endocrine tumors. The term 'crypt cell carcinoma' has been used for them, and though perhaps more accurate than considering them carcinoids, has not been a successful competitor. The ICD-O code for goblet cell carcinoid is 8243/3.

See also

• Carcinoid syndrome

External links

• Caring for Carcinoid Foundation
• http://www.netumoradvisor.org
• http://www.carcinoid.com
• The Carcinoid Cancer Foundation