Carcinoid

Carcinoid tumours are enigmatic, slow growing malignancies, which occur most frequently (74%) in the gastrointestinal tract. In recent years, it has become apparent that the term 'carcinoid' represents a wide spectrum of different neoplasms originating from a variety of different neuroendocrine cell types.

Clinical picture

Clinical manifestations are often vague or absent. Nevertheless, in approximately 10% of patients the tumours secrete bioactive mediators, which may engender various elements of characteristic carcinoid syndrome. The carcinoid syndrome results from secretion of 5HT (5-hydroxytryptamine) and bradykinnin and prostaglandins and clinically manifests itself with abdominal pain, severe diarrhoea and flushing. In many instances the neoplasms are detected incidentally at the time of surgery for other gastrointestinal disorders.

Pattern of spread

The tendency for metastatic spread correlates with tumour size, and is substantially higher in lesions larger than 2.0 cm. An association with noncarcinoid neoplasms is ascribed in 8-17% of lesions (113). The major sites of spread include the liver and mesenteric lymph nodes. Carcinoids are curious, yellow coloured tumours arising mainly from the neurosecretory cells in the appendix and caecum. Only in 25% of the carcinoids is the tumour is functional, particularly where hepatic metastases are present.

Investigation

Carcinoid lesions are usually identified histologically by their affinity for silver salts, by general neuroendocrine markers, or more specifically by immunocytochemistry using antibodies against their specific cellular products. Within the gut, the most frequent sites are the small bowel (29%), the appendix (19%) and rectum (13%).

Surgery

Treatment consists of radical surgical excision of the tumour, although gastric (type I and II) and rectal carcinoids may be managed with local excision (113).

Chemotherapy

Carcinoid tumours are not uncommon. Single active agents with 5FU, streptozotocin, mitomycin C, cyclophosphomide, methotrexate, A interferon and doxorubicin have been disappointing although studies have claimed a response rate of 30-55%. Combination chemotherapy has equally been disappointing. Medical therapies with somatostatin analogues, omeprazole, and locoregional tumor ablation have made a positive impact on curative and palliative therapy (114). Long-acting somatostatin analogs, such as octreotide, comprise the therapeutic modality of choice for the symptomatic relief of flushing and diarrhoea in patients with carcinoid syndrome. In patients with gastrin-producing duodenal carcinoids (gastrinoma), gastric acid hypersecretion are perfectly controlled by proton pump inhibitors. Antiproliferative medical strategies to control the growth of metastatic carcinoid tumours include long-acting somatostatin analogs, interferon alpha, and the combination of the two. However, the success rate is less than 50%, and it is questionable whether true tumour regression can be expected (115). Chemotherapy, including etoposide and cisplatin, has been shown to be effective only for purely differentiated neuroendocrine carcinomas and not for slowly growing carcinoids (115).

Prognosis

Overall 5-year survival is excellent for carcinoids of the appendix (86%) and rectum (72%), whereas small intestinal (55%), gastric (49%) and colonic carcinoids (42%) exhibit a far worse prognosis (113).

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