Carcinoid neoplasm (gastrointestinal)

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Carcinoid tumours are tumors of endocrine cells, and occur in a variety of organs, including the gastrointestinal tract, lung and the endocrine organs. In the GI tract, these neoplasms arise from endocrine cells widely distributed within the mucosa of the entire GI tract. These endocrine cells produce a variety of different hormones, depending on their location. For example, endocrine cells in the stomach produce histamine and gastrin, while most endocrine cells in the small intestine produce serotonin.

Carcinoid tumors are all potentially malignant tumours. If small and removed early, recurrence and metastases do not occur, while larger tumors are usually clearly malignant and capable of widespread metastases. Most carcinoids are found in the appendix, where they are usually discovered incidentally on pathological examination of an appendectomy specimen removed for appendicitis. The next most common site is the ileum, and it is the ileal carcinoids that usually give rise to the carcinoid syndrome.

Pathologically, carcinoids typically appear as yellow nodules within the wall of the affected organ. As the tumours grow, mucosal ulceration may occur and local lymph node spread will become evident.

Patients with carcinoid tumours may present with symptoms of obstruction, bleeding or metastases, or patients can present with the carcinoid syndrome.

The carcinoid syndrome arises when there are hepatic metastases of carcinoid tumor usually from the ileum. The classic clinical features are diarrhea, bronchospasm, episodic flushing, abdominal pain and right heart failure. Serotonin released by carcinoid tumors is metabolized to 5-hydroxyindoleacetic acid (5-HIAA) which can be measured in the urine.

The overall prognosis for patients with a carcinoid tumor is related to the tumor size, depth of invasion and its location. In general, appendiceal carcinoids are rarely malignant, and they can be treated by surgical resection.