The Gastrointestinal (Digestive) System
The digestive system processes food for energy and rids the body of solid waste. After food is chewed and swallowed, it enters the esophagus, a tube that carries food through the neck and chest to the stomach. The esophagus joins the stomach just beneath the diaphragm (the breathing muscle under the lungs). The stomach is a sac-like organ that holds food and begins the digestive process by secreting gastric juice. The food and gastric juices are mixed into a thick fluid, which is then emptied into the small intestine.
The small intestine continues breaking down the food and absorbs most of the nutrients. It is the longest section of the gastrointestinal (GI) tract, measuring more than 20 feet. The small intestine then joins the colon (large intestine). This is a wider, muscular tube about 5 feet long. The appendix is found near the junction of small intestine and colon. The colon absorbs water and mineral nutrients from the food matter and serves as a storage place for waste. The waste left after this process goes into the rectum. From there it passes out of the body through the anus.
The Diffuse Neuroendocrine System
Carcinoid tumors start from cells of the diffuse neuroendocrine system. This system consists of cells that are like nerve cells in certain ways and like hormone-making endocrine cells in other ways. These cells do not form an actual organ like the adrenal or thyroid glands. Instead, they are scattered throughout other organs like the esophagus, stomach, pancreas, intestines, and lungs. When neuroendocrine tumors develop in the pancreas, they are known as pancreatic islet cell tumors. Because of the size of the digestive system, it has the most neuroendocrine cells of any organ. This may explain why carcinoid tumors most often start in the digestive system.
Neuroendocrine cells help control the release of digestive juices and the speed at which food moves in the GI tract, and they may help control the growth of other types of digestive system cells.
Carcinoid (Neuroendocrine) Tumors and Cancers
Like most cells of the body, GI tract neuroendocrine cells sometimes go through certain changes that cause them to grow too much and form tumors. These are known as neuroendocrine tumors and neuroendocrine cancers.
In 2000, the World Health Organization (WHO) revised its classification of carcinoids. Before that time, most abnormal growths of neuroendocrine cells were called carcinoids. The WHO now divides these growths into neuroendocrine tumors (growths that are benign or have uncertain potential to spread to other parts of the body, and which may also be called carcinoids) and neuroendocrine cancers (which spread to other parts of the body). The WHO also subdivides neuroendocrine cancers (also known as neuroendocrine carcinomas) into well differentiated (tending to be less aggressive) and poorly differentiated (tending to be more aggressive) groups. Some doctors do not use this new terminology and use the term carcinoid to refer to either neuroendocrine tumors or well differentiated neuroendocrine cancers.
Neuroendocrine tumors and cancers act like the cells they come from. They often release certain hormone-like substances into the bloodstream. In about 1 out of 10 people with carcinoid tumors, they spread and grow very large and release high amounts of those hormones. This can cause symptoms such as facial flushing (redness and warm feeling), wheezing, diarrhea, and a fast heartbeat. These symptoms are grouped together and called the carcinoid syndrome. While most types of cancer cause symptoms only in the organs they start in or spread to, neuroendocrine tumors and neuroendocrine cancers can cause symptoms throughout the body.
Most tumors in the GI tract start from different glandular cells (the kind of gland cell that produce mucus rather than hormones) of the inner lining of the digestive system. These tumors can be either adenomas (benign) or adenocarcinomas (malignant). They are quite different from carcinoid tumors in their symptoms, their prognosis (course of the disease and outlook for survival), and their treatment. For these reasons, it is important for doctors to find out whether a patient has a neuroendocrine tumor or neuroendocrine cancer, an adenoma, an adenocarcinoma, some other type of tumor, or a non-cancerous condition. And it is important for patients to understand that neuroendocrine tumors and neuroendocrine cancers are not the same as other, more common types of GI tract tumors.
Do We Know What Causes Gastrointestinal Carcinoid Tumors?
Researchers have made great progress in understanding how certain changes in DNA can cause normal cells to become cancerous. DNA is the chemical in each cell that carries our genes - the instructions for how our cells function. We resemble our parents because they are the source of our DNA. But DNA affects more than our outward appearance. Some genes contain instructions for controlling when our cells grow and divide. Certain genes that promote cell division are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA mutations (defects) that turn on oncogenes or turn off tumor suppressor genes.
Mutations of 2 tumor suppressor genes are responsible for many inherited cases of neuroendocrine tumors and neuroendocrine cancers. Most inherited cases are due to changes in the MEN1 gene. A smaller number are caused by inherited changes in the NF1 gene.
Most cases of neuroendocrine tumors and neuroendocrine cancers are caused by DNA mutations of oncogenes or tumor suppressor genes that occur after a person is born, rather than having been inherited. These mutations often affect the MEN1 gene, the same gene that is responsible for most familial neuroendocrine tumors and neuroendocrine cancers. In many other types of cancer, researchers have shown that these acquired mutations are the result of cancer-causing chemicals in our environment, diet, or tobacco smoke. Relatively little is known, however, about factors that cause new mutations in genes that lead to neuroendocrine tumors and neuroendocrine cancers.
Doctors do know that carcinoid tumors start out very small and grow slowly. When patients have parts of their stomach or small intestine removed to treat other diseases, taking a close look under the microscope often shows small groups of neuroendocrine cells that look like tiny carcinoids. Researchers still do not know why some remain so small and others begin to grow and become large enough to cause symptoms.
Can Gastrointestinal Carcinoid Tumors Be Found Early?
Because carcinoid tumors usually grow and spread slowly, about half of all gastrointestinal carcinoid tumors are found at an early or localized stage, usually before they cause any problems.
Incidental Diagnosis of Carcinoid Tumors
In many cases, carcinoid tumors are found incidentally when looking for something else. The tumors don't cause any symptoms but are found during tests done for other diseases or because parts of the digestive system are removed to treat other diseases.
For example, a person with stomach symptoms may have a test called an upper endoscopy, where the doctor looks at the stomach lining through a flexible lighted tube. During this test, the doctor may incidentally notice a small bump in the stomach wall that turns out to be a carcinoid tumor.
Sometimes during colorectal cancer screening a routine sigmoidoscopy or colonoscopy (looking at the large bowel through a flexible lighted tube) will incidentally find a small carcinoid tumor.
When a person's appendix is removed to treat appendicitis (inflammation of the appendix), doctors may incidentally find a small carcinoid, as well as the expected inflammation. Some studies have found that about 1 of every 300 people who have appendix surgery done for other diseases turn out to have a tiny carcinoid near the tip of their appendix. In most of these cases, the carcinoid was too small to have caused any symptoms.
How Are Gastrointestinal Carcinoid Tumors Treated?
This information represents the views of the doctors and nurses serving on the American Cancer Society's Cancer Information Database Editorial Board. These views are based on their interpretation of studies published in medical journals, as well as their own professional experience.
The treatment information in this document is not official policy of the Society and is not intended as medical advice to replace the expertise and judgment of your cancer care team. It is intended to help you and your family make informed decisions, together with your doctor.
Your doctor may have reasons for suggesting a treatment plan different from these general treatment options. Don't hesitate to ask him or her questions about your treatment options.
Once a neuroendocrine tumor/cancer is found and staged, the cancer care team will suggest one or more treatment plans. This is an important decision, so you should take time and think about all of your options.
The main factors in selecting treatment options for a gastrointestinal (GI) neuroendocrine tumor/cancer are:
- its size and location
- whether it has spread to lymph nodes, liver, bones, or other organs
- whether you have any other serious medical conditions
- whether the tumor is causing bothersome symptoms
It is often a good idea to seek a second opinion. A second opinion may provide more information and help you feel more confident about the treatment plan that is chosen.
The first part of this section describes the various types of treatments used for GI neuroendocrine tumors/cancers. This is followed by a description of the most common approaches used for these tumors/cancers based on their stage and primary site.
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