Carcinoid tumors

Carcinoid tumors are neoplasms derived from neuroendocrine cells and are widely distributed throughout the body in almost any organ. The traditional classification of carcinoid tumors includes foregut tumors with primaries located in the lung, stomach, or proximal duodenum, as well as the thymus; midgut tumors arising from the jejunum, ileum and proximal colon (appendix); and hindgut carcinoids (originating in the distal part of the colon and rectum. Foregut derivatives (except for the pharynx, the respiratory tract, and most of the esophagus) are mainly based on the celiac artery, midgut derivatives are based on the superior mesenteric artery, and hindgut derivatives are supplied by the inferior mesenteric artery. Carcinoid tumors, while observed in approximately 1 % of appendectomy specimens, are the most common tumor of the vermiform appendix. The most common locations for carcinoid tumors are the appendix and distal ileum, followed by stomach, bronchopulmonary, and rectal. Carcinoid tumors produce a number of biologically active substances such as chromogranin A and 5-HIAA, which can be measured and used for diagnostic purposes. Octreoscan is the most widely used imaging modality for carcinoid An appendectomy is the treatment for appendiceal tumors less than 2 cm in diameter, whereas a right hemicolectomy is indicated for larger or more aggressive tumors. The general principle of surgical resection for tumors in other locations includes complete resection of the tumor with lymphadenectomy of the regional lymph nodes. Tumor debulking may play a palliative role in selected patients. Liver resection and transplantation have been shown to have excellent long-term survival for patients with isolated, resectable hepatic metastasis Overall prognosis is greater than 80 % after 10 years for appendiceal carcinoid tumors that had no evidence of metastatic disease. Carcinoid tumors of the small bowel have an overall 5-year survival rate of 50–60 %. Bronchial carcinoids can be of either typical or atypical histology and carry a 5-year survival rate of almost 90 % if typical but only 60 % for atypical subtypes. Foregut carcinoids of the stomach are divided by type with types 1 and 2 having an almost 100 % 5-year survival rate while type 3 tumors carry a 50 % 5-year survival rate and type 4 are often unresectable and carry the worst prognosis. Hindgut colorectal carcinoid tumors tend to be diagnosed later than small bowel carcinoid tumor and are associated with a worse prognosis; its 5-year survival rate is 40–50 %. Somatostatin analogs are the mainstay of medical therapy for patients with advanced disease. Systemic chemotherapy has not shown benefit over treatment with somatostatin analogs alone; however, novel agents such as radiolabeled somatostatin analogs and bevacizumab have shown promise as adjuvant treatment options.