NETs can arise in different organs and from different cell types, and so present a clinical challenge to physicians owing to their diversity and the variety of symptoms they cause. Functioning NETs are characterized by the hormones they produce and/or the symptoms they cause; clinical symptoms are typically observed following metastasis to the liver.
Many functioning NETs release vasoactive peptides and amines, such as serotonin and tachykinins, into the systemic circulation and cause a characteristic set of symptoms called 'carcinoid syndrome', which occurs in approximately 10% of patients with metastatic NETs. It is characterized by flushing (63–94% of patients), diarrhea (68–84%), abdominal pain (10–55%), telangiectasia (25%) and bronchoconstriction (3–19%).[11,23,24] A recent study found that patients with NETs report worse health-related quality of life (HRQoL) than the general population, primarily due to the presence of carcinoid syndrome. Using the RAND-36 scale, where the general mean population score for a health parameter is 50 and lower scores indicate worse HRQoL, patients with NETs and carcinoid syndrome (n = 328) scored 39.4 for physical functioning compared with 44.5 in patients with NETs without carcinoid syndrome (n = 115) and 50.8 in subjects without NETs (n = 83).
Carcinoid crisis is the most immediate life-threatening complication of carcinoid syndrome and is thought to result from a massive release of bioactive products from the tumor. Crises can occur spontaneously, but often arise in response to stress, anesthesia, chemotherapy or surgery. Symptoms are an exacerbation of the usual clinical symptoms of carcinoid syndrome, including severe flushing with or without bronchospasm, tachycardia and hypo/hypertension. Failure to effectively manage carcinoid syndrome can lead to exposure of the heart to high levels of vasoactive substances released from hepatic metastases, which causes carcinoid heart disease; between 10–20% of patients with carcinoid syndrome have heart disease at diagnosis. Carcinoid heart disease is characterized by plaque-like, fibrous thickening of the endocardium (classically on the right side of the heart); tricuspid and pulmonary valves; right-sided carcinoid heart disease is associated with substantial morbidity and mortality.
Expert Rev Endocrinol Metab. 2011;6(1):49-62. © 2011 Expert Reviews Ltd.
Cite this: Management of Neuroendocrine Tumors: Current and Future Therapies - Medscape - Jan 01, 2011.