What is colon cancer?
Colon cancer forms in the tissues of the colon, which is part of the large intestine.
The colon is part of the body's digestive system, which is made up of the esophagus, stomach, and the small and large intestines. The first six feet of the large intestine are called the colon. The remaining several inches of the large intestine form the rectum.
Different types of cancer can develop in the colon. Most colon cancers are adenocarcinomas, which are cancers from glandular tissue. Other cancer types that can occur in the colon include
carcinoid tumors, small cell carcinomas, and
gastrointestinal stromal tumors (GIST).
The focus of this information is on colon cancers that are adenocarcinomas.
Colon and rectal cancers are the fourth most common cancers diagnosed in the United States. Survival after diagnosis has been gradually increasing in the past decade. There are several reasons for this. First, screening programs can catch the disease in its pre-cancerous or early stages, which are more curable. Second, there are better treatments, both surgical techniques and chemotherapies, including targeted therapies.
Our team has been a leader in
clinical trials for various treatments for colon cancer to improve outcomes for patients and survivors.
When detected early, colon cancer is a very treatable form of cancer. The earlier it is found, the more likely it is that the cancer will be cured. As the cancer becomes more advanced, the cure rate declines, but it may still be treatable for long periods of time.
Most colon cancers start as polyps, or growths in the colon. Over time, some, but not all polyps change into cancers. Polyps that have a higher risk becoming cancer are known as adenomas.
- The reason screening is so important is that finding polyps before they become cancer reduces the risk of developing colon cancer by at least 90 percent.
- Finding ways to prevent polyps from forming is an important area of ongoing research at Dana-Farber/Brigham and Women's Cancer Center.
- Together, colon and rectal cancer are the fourth most common type of cancers in the United States.
- Colon cancer is mainly a disease of developed countries with a Western culture.
- The disease is most often diagnosed in people 50 and older. However, it can affect those younger and appears to be increasing among younger people, though the reason for this is not known.
- Colon cancer affects men and women about equally.
Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors does not mean that you will not get cancer. Risk factors for colon cancer include:
- Increasing age: Most people who develop colon cancer are 50 or older.
- A family history of cancer of the colon or rectum.
- Certain hereditary conditions, such as
familial adenomatous polyposis, and hereditary nonpolyposis colon cancer, called Lynch syndrome.
- A history of inflammatory bowel disease (IBD), such as ulcerative colitis and Crohn's disease
- A personal history of cancer of the colon, rectum, ovary, endometrium, or breast.
- A personal or family history of adenomas (polyps) in the colon or rectum. These growths can be pre-cancerous. Most adenomas will not turn into cancer. However, regular screening to remove them reduces the risk of developing colon cancer.
- Environmental and lifestyle-related factors, such as lack of exercise, obesity, smoking, and alcohol consumption.
- Our team works on research with the Harvard T.H. Chan School of Public Health and has published many landmark papers on diet, lifestyle, and the risk of colon cancer.
- A diet high in red and processed meat.
- Low vitamin D levels.
According to research conducted at Dana-Farber/Brigham and Women's Cancer Center, 70 to 80 percent of colon cancer cases may be prevented through exercise, weight control, limiting alcohol consumption, and taking aspirin and vitamin D.
People with a family history of colon cancer and/or other cancers in several close relatives across generations – especially if these cancers occur at a young age – may benefit from genetic counseling and testing.
Learn more about the importance of
good nutrition in cancer prevention for cancer patients and survivors.
Learn more about having a family history of cancer and genetic risk factors through our
Center for Cancer Genetics and Prevention,.
Symptoms and signs
Potential symptoms and signs of colon cancer include:
- A change in bowel habits.
- Blood (either bright red or very dark) in the stool.
- Diarrhea, constipation, or feeling that the bowel does not empty all the way.
- Stools that are narrower than usual.
- Frequent gas pains, bloating, fullness, or cramps.
- Weight loss for no known reason.
- Feeling very tired.
- Anemia (low red blood cell count).
It is important to know that these symptoms and signs can have many causes, and may not be due to cancer. However, it is important that you discuss these symptoms or signs with your doctor.
Further, many people, particularly those with polyps or early stages of colon cancer, may not have any symptoms or show any signs, making it difficult to detect without regular screening. Several screening methods make it possible to find some cancers before symptoms appear.
Screening and prevention
Screening for colon cancer helps prevent the disease and decrease the number of deaths from it. Some tests to find polyps can actually prevent the development of cancer because doctors can remove the growths before they become problems.
There are several ways to screen for colon cancer. Each type of test has advantages and disadvantages, due to risks from the test and the sensitivity/accuracy of the test. You should talk to your doctor about when to begin screening for colon cancer, what test to have, the benefits and drawbacks of each test, how often to undergo screening, and when to stop screening.
Options for screening include:
- Fecal occult blood testing: A test to check stool (solid waste) for blood that can be seen only with a microscope. Small samples of stool are placed on special cards and returned to the doctor or laboratory for testing.
- Sigmoidoscopy: A procedure to look inside the rectum and sigmoid (lower) colon for polyps (small areas of bulging tissue), other abnormal areas, or cancer. A sigmoidoscope is inserted through the rectum into the sigmoid colon. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It also has a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.
- Colonoscopy: A procedure to look inside the rectum and entire colon for polyps, abnormal areas, or cancer. A colonoscope is inserted through the rectum into the colon. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It will also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.
- Virtual colonoscopy: A procedure that uses a series of x-rays called computed tomography (CT) to make a series of pictures of the colon. A computer puts the pictures together to create detailed images that may show polyps and anything else that seems unusual on the inside surface of the colon. This test is also called colonography, or CT colonography.
- DNA test: A test of the stool for small pieces of DNA that come from cells lining the colon and rectum. It looks for abnormal DNA that may be due to a cancer.
- Double-contrast barium enema: A series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series. It is rarely used anymore.
National Cancer Institute website describes these tests in more detail.