| Carcinoid | |
|---|---|
 | |
| Picture of acarcinoid tumor (center of image) that encroaches into the lumen of thesmall bowel (pathology specimen). The prominent folds areplicae circulares, a characteristic of the small bowel. | |
| Specialty | Oncology |
Acarcinoid (alsocarcinoid tumor) is a slow-growing[1] type ofneuroendocrine tumor originating in the cells of theneuroendocrine system. In some cases,metastasis may occur. Carcinoid tumors of the midgut (jejunum,ileum,appendix, andcecum) are associated withcarcinoid syndrome.
Sometimes, carcinoids causeparaneoplastic syndromes, which involve discharge ofserotonin and othervasoactive substances from well-differentiated carcinoids.[2][3] A neuroendocrine paraneoplastic syndrome involves neoplastic secretion of functionalpeptides,hormones,cytokines,growth factors, and/or immunecross-reactivity between tumor tissues and normal host tissues, resulting in asyndrome of clinical signs and symptoms.[4]
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 therectum andstomach. 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. The median age at diagnosis for all patients with neuroendocrine tumors is 63 years.
While most carcinoids are asymptomatic through the natural life and are discovered only upon surgery for unrelated reasons (so-calledcoincidental carcinoids), all carcinoids are considered to have malignant potential.
About 10% of carcinoids secrete excessive levels of a range ofhormones, most notably serotonin (5-hydroxytryptamine), causing:
The outflow of serotonin can cause a depletion oftryptophan leading toniacin deficiency.Niacin deficiency, also known aspellagra, is associated with dermatitis, dementia, and diarrhea.
This constellation of symptoms is calledcarcinoid syndrome or (if acute)carcinoid crisis. Occasionally,haemorrhage or the effects of tumor bulk are the presenting symptoms. The most common originating site of carcinoid is the small bowel, particularly the ileum; carcinoid tumors are the most common malignancy of the appendix. Carcinoid tumors may rarely arise from the ovary or thymus.[6]
They are most commonly found in themidgut at the level of theileum or in theappendix. The next most commonly affected area is therespiratory tract, with 28% of all cases—per PAN-SEER data (1973–1999). Therectum is also a common site.
Carcinoid tumors areapudomas that arise from theenterochromaffin cells throughout the gut. Over two-thirds of carcinoid tumors are found in thegastrointestinal tract.[7]
Carcinoid tumors are also found in thelungs.
Metastasis of carcinoid can lead tocarcinoid syndrome. This is due to the over-production of many substances, includingserotonin, which are released into the systemic circulation, and which can lead to symptoms of cutaneous flushing,diarrhea,bronchoconstriction, and right-sidedcardiacvalve disease. It is estimated that less than 6% of carcinoid patients will develop carcinoid syndrome, and of these, 50% will have cardiac involvement.[8]
This is considered to be a hybrid between anexocrine andendocrine tumor 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 tumor nests interspersed among themuscle andstroma of the appendiceal wall extending up the shaft of the appendix. This makes the lesion difficult to suspect grossly and difficult to measure. Small tumor nests may be camouflaged amongst the muscle or in periappendiceal fat;cytokeratin preparations best demonstrate the tumor 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 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.
Carcinoid syndrome involves multiple tumors in one out of five males. The incidence of gastric carcinoids is increased inachlorhydria,Hashimoto's thyroiditis, andpernicious anemia.
Surgery, if feasible, is the only curative therapy. If the tumor has metastasized (most commonly, to theliver) and is considered incurable, there are some promising treatment modalities, such as theradiopharmaceuticalsLutetium (177Lu) DOTA-octreotate) and 131I-mIBG (meta iodo benzyl guanidine[9]) 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 orlanreotide (somatostatin analogues) may decrease the secretory activity of the carcinoid, and may also have an anti-proliferative effect.Interferon treatment is also effective, and usually combined with somatostatin analogues.
As the metastatic potential of a coincidental carcinoid is probably low, the current recommendation is for follow up in 3 months with CT or MRI, labs for tumor markers such as serotonin, and a history and physical, with annual physicals thereafter.
They were first characterized in 1907 bySiegfried Oberndorfer, aGermanpathologist at theUniversity of Munich, who coined the termkarzinoide, or "carcinoma-like", to describe the unique feature of behaving like abenign tumor despite having amalignant appearance microscopically. The recognition of their endocrine-related properties was later described by Gosset and Masson in 1914, and these tumors are now known to arise from the enterochromaffin (EC) and enterochromaffin-like (ECL) cells of the gut. Some sources creditOtto Lubarsch with the discovery.[10]
In 2000, theWorld Health Organization redefined "carcinoid", but this new definition has not been accepted by all practitioners.[11] This has led to some complexity in distinguishing between carcinoid and other neuroendocrine tumors in the literature. According to the American Cancer Society, the 2000 WHO definition states:[11]
The WHO now divides these growths into neuroendocrine tumors and neuroendocrine cancers. Neuroendocrine tumors are growths that look benign but that might possibly be able to spread to other parts of the body. Neuroendocrine cancers are abnormal growths of neuroendocrine cells which can spread to other parts of the body.
Specific torodents, chronically reducedgastric acid secretion encourages carcinoid development.[12]: 812
{{cite book}}:|work= ignored (help)Cunningham JL, Janson ET (2011). "The Hallmarks of Ileal Carcinoids".Eur J Clin Invest.41 (12):1353–60.doi:10.1111/j.1365-2362.2011.02537.x.PMID 21605115.S2CID 31500259.
