Carcinoid tumor and Carcinoid syndrome

       Carcinoid tumor
            A carcinoid tumor is a tumor that develops from enterochromaffin cells. Enterochromaffin cells are hormone-producing cells that normally are found in the small intestine, appendix, colon, rectum, bronchi, pancreas, ovaries, testes, bile ducts, liver, as well as other organs. Enterochromaffin cells produce many types of hormones for example, histamine, serotonin, dopamine, tachykinins, and other substances that have profound effects on the circulatory system (heart and blood vessels), the gastrointestinal tract, and the lungs. For example, serotonin can cause diarrhea, histamine wheezing, and tachykinins flushing due to dilation of blood vessels.
Since carcinoid tumors develop from enterochromaffin cells, they frequently retain the capability of producing the same hormones, often in large quantities. When these hormones circulate in the blood, they can cause symptoms of carcinoid syndrome, which is discussed later.
The important characteristic of carcinoid tumors that sets them apart from other gastrointestinal tract tumors is their potential to cause the carcinoid syndrome. Most other gastrointestinal tract tumors (such as colon cancers or small bowel lymphomas) cause symptoms primarily due to their local effects on the intestines such as abdominal pain, intestinal bleeding, and intestinal obstruction. Although carcinoid tumors may also cause these local symptoms, they may also produce and release hormones that cause the carcinoid syndrome. Often, symptoms of the carcinoid syndrome can be more devastating than the local symptoms.


 Carcinoid syndrome
The carcinoid syndrome is a combination of symptoms caused by the hormones released by the tumors into the blood stream. The symptoms of the carcinoid syndrome vary depending on which hormones are released by the tumors. The common hormones released are serotonin, bradykinin (a molecule produced by enzymes at the site of an injury and then binds to receptors to cause pain), histamine, and chromogranin A (a general marker for neuroendocrine tumors). Typical carcinoid symptoms include:
• flushing
• diarrhea
• abdominal pain
• and wheezing due to bronchospasm (airway narrowing)
• valvular heart disease
• surgery can provoke a complication known as carcinoid crisis.
Flushing
Flushing is the most common symptom of carcinoid syndrome. An estimated 90% of the patients have flushing some time during their illness. Flushing is characterized by redness or purple discoloration of face and neck (or upper body) accompanied by a warm sensation. Episodes of flushing typically occur suddenly, either spontaneously or brought on by emotional stress, physical stress, or drinking alcohol. Episodes of flushing can last minutes to hours. Flushing can be accompanied by palpitations, low blood pressure, or fainting if blood pressure becomes too low to supply blood to the brain. Rarely, flushing can be accompanied by high blood pressure. Hormones responsible for flushing have not been clearly identified; possible candidates include serotonin, bradykinin, and substance P.
Diarrhea
Diarrhea is the second most common symptom of carcinoid syndrome. An estimated 75% of patients with carcinoid syndrome have diarrhea. Diarrhea often occurs with flushing but also can occur alone. Diarrhea in the carcinoid syndrome is most likely caused by the hormone serotonin. Medications that block the action of serotonin such as ondansetron (Zofran) often alleviates the diarrhea. Sometimes diarrhea in the carcinoid syndrome can be due to a local effect of the tumor obstructing the small intestine.
Heart disease
Heart disease occurs in an estimated 50% of patients with the carcinoid syndrome. Carcinoid syndrome typically causes scarring and stiffness of the tricuspid and pulmonic valves of the right side of the heart. Stiffness of these two valves decreases the ability of the heart to pump blood from the right ventricle to the lungs and to the rest of the body and leads to heart failure. Typical symptoms of heart failure include an enlarged liver (due to the backup of blood returning to the failing heart which is unable to pump all of the blood returning to it), swelling of the feet and ankles (edema), and swelling of the abdomen due to fluid accumulation (ascites). The damage to the tricuspid and pulmonic valves of the heart in the carcinoid syndrome is most likely caused by prolonged exposure to high levels of serotonin in the blood.
Carcinoid crisis
Carcinoid crisis is a dangerous condition that can occur at the time of surgery. It is characterized by a sudden and profound drop in blood pressure causing shock, sometimes accompanied by an abnormally fast heart rate, high blood glucose, and severe bronchospasm. Carcinoid crisis can be fatal. The best way to prevent carcinoid crisis is to treat patients undergoing surgery with somatostatin (see below) before surgery begins.
Wheezing
Wheezing occurs in approximately 10% of the patients with carcinoid syndrome. It is a result of bronchospasm (constriction of the bronchial airways) caused by hormones released by the carcinoid tumors.
Abdominal pain
Abdominal pain is common in patients with carcinoid syndrome. The pain may be due to tumor metastases in the liver, tumor invading neighboring tissues and organs.