Carcinoid syndrome is a paraneoplastic syndrome comprising the signs and symptoms that occur secondary to carcinoid tumors. The syndrome includes flushing and diarrhea, and less frequently, heart failure, vomiting and bronchoconstriction. It is caused by endogenous secretion of mainly serotonin and kallikrein. Signs and symptoms
The carcinoid syndrome occurs in approximately 5% of carcinoid tumors and becomes manifest when vasoactive substances from the tumors enter the systemic circulation escaping hepatic degradation. If the primary tumor is from the gastrointestinal tract (hence releasing serotonin into the hepatic portal circulation), carcinoid syndrome generally does not occur until the disease is so advanced that it overwhelms the livers ability to metabolize the released serotonin. Flushing: The most important clinical finding is flushing of the skin, usually of the head and the upper part of thorax. Diarrhea: It may be associated with abdominal cramping. This symptom is due to the action of serotonin, histamine, and gastrin
Abdominal pain: It is due to hepatomegaly, small bowel obstruction or lack of oxygen to small bowel. Bronchoconstriction, which may be histamine or serotonin-induced, affects about 15% of those having carcinoid syndrome and often accompanies flushing, sneezing, and shortness of breath. Carcinoid heart disease: About 19% to 60% of the those affected by carcinoid syndrome develop carcinoid heart disease. Serotonin induces fibrosis in valves of the right heart especially tricuspid valve. Pathophysiology
Carcinoid tumors produce several vasoactive substances, most prominently serotonin. It is commonly thought that serotonin is the cause of the flushing, but this is only partially correct.
A tracer agent of Indium 111 is injected into a vein where then the tumors absorb the radionuclide Indium 111 and become visible on the scanner. Only the tumors absorb the somatostatin agent Indium 111 making the scan highly effective. Treatment
For symptomatic relief of carcinoid syndrome:
Octreotide (a somatostatin analogue which decreases the secretion of serotonin by the tumor and, secondarily, decreases the breakdown product of serotonin (5-HIAA))
Telotristat ethyl (Xermelo) along with a somatostatin analogue in patients not responding to somatostatin analogue monotherapy. It is a tryptophan hydroxylase inhibitor and reduces the production of serotonin. Peptide receptor radionuclide therapy (PRRT) with lutetium-177, yttrium-90 or indium-111 labeled to octreotate is highly effective
Methysergide maleate (antiserotonin agent but not used because of the serious side effect of retroperitoneal fibrosis)
Cyproheptadine (an antihistamine drug with antiserotonergic effects)Alternative treatment for qualifying patients:

Surgical resection of tumor and chemotherapy (5-FU and doxorubicin)
Endovascular, chemoembolization, targeted chemotherapy directly delivered to the liver through special catheters mixed with embolic beads (particles that block blood vessels), used for patients with liver metastases. Uncertainties
Disease progression is difficult to ascertain because the disease can metastasize anywhere in the body and can be too small to identify with any current technology. Markers of the condition such as chromogranin-A are imperfect indicators of disease progression. Prognosis
Prognosis varies from individual to individual. It ranges from a 95% 5-year survival for localized disease to an 80% 5-year survival for those with liver metastases. The average survival time from the start of octreotide treatment has increased to about 12 years.