Colon Cancer

Am Fam Physician. 2018;97(10):online

See related article on colorectal cancer

What is colon cancer?

Colon cancer is a tumor of the large intestine (colon). It is the third most common cause of cancer-related death in the United States. However, most people with colon cancer get better if the cancer is found early.

Rectal cancer is a type of colon cancer that starts at the end of the large intestine, which is called the rectum. The term colorectal cancer is used for cancer of the colon or rectum.

What are the symptoms?

Colon cancer can cause blood in the stool, stomach pain, and a change in bowel movements (such as a change in the size of your stool). Some people do not have any symptoms. If you do not have symptoms, it is more likely that the tumor will not be found and will continue to grow. Screening tests can find cancer and small tumors called polyps (POL-ips) that can turn into cancer over time.

Who should be screened?

Healthy people 50 years and older should get screened. You should continue screening until you are 75 years old. If you have symptoms of colon cancer or if you are at risk of colon cancer, your doctor may suggest getting screened before 50 years of age. You are at higher risk of colon cancer if you have a parent or sibling who has or had colon cancer, polyps, or other less common conditions, such as inflammatory bowel disease.

What are some colon cancer screening tests?

There are several kinds of screening tests for colon cancer. Some can be done at home, and some are done at a doctor's office. They range in cost and the type of preparation needed before the test.

Fecal immunochemical test (FIT). This test is done at home once a year. You take a single stool sample to your doctor for testing. You can get a testing kit at the pharmacy or from your doctor. This test is not affected by food or medicine. If the test is abnormal, you will still need to have a colonoscopy (ko-lun-OS-ko-pee).
Colonoscopy. This test is done every 10 years. For this test, your doctor will give you medicine to make you sleepy. He or she will then put a thin tube connected to a video camera into your rectum to look at your whole colon. You will have to take laxatives the day before the test to clean out your colon. If polyps are found during the test, they can usually be removed right away. You will probably miss a day of work, and someone will have to drive you home after the test. This test may not be available at smaller hospitals. Colonoscopy is the most accurate test, but it is also the most expensive. It causes more injuries than the other tests (15 people will be injured for every 1,000 people who have the test). If your colon is injured during the test, you may need surgery to repair it.
Guaiac-based fecal occult blood test. This test is done at home once a year. You will need to take a stool sample from three bowel movements in a row and give it to your doctor for testing. You can get a testing kit at the pharmacy or from your doctor. This test decreases death from colon cancer. But, it has low accuracy and works only if you do the test every year. Eating certain foods and taking certain medicines may result in a false-positive test; these should be avoided before stool collection. If the test is abnormal, you will still need to have a colonoscopy.
Multitargeted stool DNA test (FIT-DNA). This test is done at home every one to three years. You take a single stool sample to your doctor for testing. You can get a testing kit at the pharmacy or from your doctor. This test is not affected by food or medicines. If the test result is abnormal, you will still need to have a colonoscopy.
Flexible sigmoidoscopy. This test is done every five years. For this test, your doctor will put a thin, lighted tube into your rectum. The tube is connected to a video camera so the doctor can look at your rectum and the lower part of your colon. You will have to take laxatives the day before or the morning of the test to clean out your colon. You will be awake during the test, and you will probably be able to go back to work after the test. This test decreases death from colon cancer and is more accurate than stool tests alone. It is safer and costs less than a colonoscopy, but it is not as accurate. If the test is abnormal, you will still need to have a colonoscopy.
CT colonography. This test is also called a “virtual” or “x-ray” colonoscopy. It is a newer test, and the best way to use it has not been decided. Also, it is not clear how safe it is compared with the other tests. For this test, compressed air is pumped into your rectum through a tube. Then, a picture is taken of your colon. You will have to take laxatives the day before the test to clean out your colon. This test is almost as good at finding large polyps as colonoscopy, but it is less accurate overall, especially for finding small polyps. If the test is abnormal, you will still need to have a colonoscopy.

How can I prevent colon cancer?

The only way to prevent colon cancer is to find polyps early and have them removed.

Eating more calcium and dairy, eating less red meat, increasing physical activity, losing weight if you are overweight, and taking statins (medicines for high cholesterol) may lower the risk of getting polyps and colon cancer.

Taking aspirin or ibuprofen may lower your risk of getting polyps and colon cancer. But, aspirin and ibuprofen may also cause kidney problems or bleeding in your stomach. Aspirin is only recommended for people 50 to 69 years of age who are at higher risk of heart disease and who are willing to take aspirin for at least 10 years to get the full benefit.

Women who have gone through menopause may lower their risk of colon cancer by taking hormones. But, hormones have side effects, including blood clots and a higher risk of breast cancer. Taking fiber, folic acid, or antioxidants (for example, vitamin A) does not change the risk of getting polyps or colon cancer.