Carcinoid tumors are the most common type of neuroendocrine tumor. An estimated 11,000 to 12,000 people are diagnosed with a carcinoid tumor each year in the United States. About two-thirds of all carcinoid tumors appear in the gastrointestinal system, particularly in the small intestine, rectum, stomach, colon, and liver.
Carcinoid tumors usually grow slowly over many years. Neuroendocrine tumors that grow slowly are called low-grade tumors. However, even low-grade carcinoid tumors can begin to grow rapidly, for reasons that are not well understood.
Risk factors for gastrointestinal carcinoid tumors include:
- a family history of multiple endocrine neoplasia type 1 (MEN1) syndrome, a rare genetic disorder that can cause the parathyroid glands, pituitary gland, and pancreas to produce too many hormones
- certain conditions that affect that stomach’s ability to produce stomach acid
Carcinoid tumors usually do not cause symptoms in the early stages. However, some patients may experience symptoms such as facial flushing, diarrhea, abdominal pain, asthma, a rash, and dark-colored stools (which indicate intestinal bleeding).
Many carcinoid tumors produce a hormone called serotonin, which can lead to a variety of symptoms known as carcinoid syndrome. One or more of the following symptoms may indicate carcinoid syndrome:
- facial flushing
- abdominal pain (caused by blockage of the intestines)
- shortness of breath or wheezing
- rapid heartbeat
- weight gain or loss
- heart valve damage
Patients with carcinoid syndrome who undergo surgery, anesthesia, or chemotherapy are at risk of experiencing a carcinoid crisis, which is a life-threatening condition caused by a sudden surge of serotonin into the bloodstream. Treatment with the hormone octreotide before any medical procedure can help prevent a carcinoid crisis from occurring. People with carcinoid syndrome are advised to wear a medical bracelet in the event of an emergency. Patients with carcinoid tumors who do not have carcinoid syndrome (i.e., the tumor does not make serotonin) are not at risk for this problem.
Many gastrointestinal carcinoid tumors are found through imaging studies performed for other health issues.
If a carcinoid tumor is suspected, and patients have symptoms of carcinoid syndrome, blood and urine tests may be used to look for abnormal amounts of hormones and other substances (peptides) produced by the tumor, including chromogranin A (a protein commonly found in many carcinoid tumors) and 5HIAA (a byproduct of serotonin found in the urine).
To confirm diagnosis, a small sample of the tumor may be obtained for examination under a microscope using either a thin needle (fine-needle aspiration biopsy) or a wider needle (core biopsy).
In addition, the following imaging tests may be performed to confirm the diagnosis, and to determine the exact location and size of the tumor, if it has spread to other organs, and whether it can be surgically removed:
Triphasic CT Scanning
Triphasic CT scanning, which provides images during three different phases of blood flow through the liver, offer a more accurate diagnosis than routine CT. These tests are often used to determine whether the tumor has spread to the liver or nearby lymph nodes.
OctreoScan (Somatostatin Receptor Scintigraphy) Imaging
Many neuroendocrine tumors absorb large amounts of somatostatin, a substance that suppresses the hormones involved in growth, metabolism, and digestion. Patients suspected of having a gastrointestinal carcinoid tumor receive an injection of octreotide, a synthetic form of somatostatin that is attached to a radioactive substance. Radiation-sensitive imaging tests reveal how much octreotide has been absorbed, indicating the presence and size of a tumor. Tumors that absorb octreotide may be treated with octreotide therapy (described below in the Treatment section).
Some neuroendocrine tumors absorb the hormone norepinephrine. Like the OctreoScan, this nuclear imaging technique involves giving patients an injection of MIBG, a protein similar to norepinephrine that is combined with a radioactive substance. Radiation-sensitive imaging tests reveal how much MIBG has been absorbed, indicating the presence of a carcinoid tumor. Tumors that absorb MIBG may be treated with MIBG radiolabeled therapy (described below in the Treatment section).
There are several treatment options for patients with a gastrointestinal carcinoid tumor. Patients may receive one or more treatments such as surgery, minimally invasive therapy, hormone therapy, chemotherapy, and radiolabeled therapy.
Surgical removal of the tumor is usually the first treatment for gastrointestinal carcinoid tumors. Tumors that have not spread (localized tumors) may be removed along with a small portion of healthy tissue surrounding the tumor. Depending on the location of the tumor and whether it has spread, additional surgery may be required to remove portions of the affected organ or nearby lymph nodes. When possible, our doctors use laparoscopic surgery to remove carcinoid tumors and nearby lymph nodes. In this procedure, the surgeon inserts a laparoscope — a thin, lighted tube with a camera on its tip — into the abdomen through a small incision. This minimally invasive approach can reduce postoperative pain and recovery time for patients. In some cases, complete removal of the tumor may not be possible. Surgery to reduce the size of the tumor may be performed only if the patient has symptoms from the tumor or in other rare circumstances.
Liver Tumor Embolization
Embolization, a localized approach to destroying liver tumors, may be used to treat gastrointestinal carcinoid tumors that spread to the liver. The portal vein channels blood and nutrients to the liver, but the hepatic artery directs blood to liver tumors. Embolization uses image guidance, such as CT or ultrasound, to inject tiny particles through a small tube, or catheter, threaded into the hepatic artery. The particles block the flow of blood to the tumor, depriving it of the nutrients and oxygen it needs to survive. Embolization may be used alone or in combination with surgery.
Patients with gastrointestinal carcinoid tumors that cannot be surgically removed may benefit from monthly injections of a synthetic hormone, octreotide, which controls hormone-related symptoms and may have the potential to slow tumor growth.
Chemotherapy is usually reserved for patients whose carcinoid tumors begin to grow during treatment with octreotide. In addition, chemotherapy may be used to treat advanced carcinoid tumors that contain fast-growing (undifferentiated) cells.
MIBG Radiolabeled Therapy
Some neuroendocrine tumors absorb a hormone called norepinephrine. These tumors may respond to a nuclear medicine technique called MIBG radiolabeled therapy. In this treatment, the patient is given an intravenous dose of MIBG, a protein that is similar to norepinephrine and is attached to a radioactive substance. The MIBG is absorbed by the tumor, permitting the radioactive substance to selectively destroy tumor cells.
Peptide Receptor Radionuclide Therapy (PRRT)
PRRT is a new nuclear medicine therapy. This treatment uses a radioactive drug called lutetium Lu 177 dotatate (Lutathera®), which is given through an IV. The drug is effective against gastrointestinal and pancreatic carcinoid tumors that have proteins called somatostatin receptors. It works by targeting the somatostatin receptors in order to bring the drug’s radioactive particles inside the cancer cells to attack from within. MSK’s doctors may recommend PRRT when surgery is not an option or when other treatments have not slowed a tumor’s growth.