Colorectal Cancer Screening

by National Cancer Institute

1. What is colorectal cancer?

Colorectal cancer is a disease in which cells in the colon or rectum become abnormal and divide without normal control or order, forming a mass called a tumor. (The colon and rectum are parts of the body's digestive system that remove water and nutrients from food and store solid waste until it passes out of the body.) Cancer cells invade and destroy the tissue around them. They can also break away from the tumor and spread to form new tumors in other parts of the body.

Colorectal cancer is the third most common type of non-skin cancer in men (after prostate cancer and lung cancer) and in women (after breast cancer and lung cancer). It is the second leading cause of cancer death in the United States after lung cancer. The rate of new cases and deaths resulting from this disease is decreasing. Still, over 147,000 new cases are diagnosed, and more than 57,000 people die from colorectal cancer each year.

2. Who is at risk for colorectal cancer?

The exact causes of colorectal cancer are not known. However, studies show that certain factors are linked to an increased chance of developing colorectal cancer:

Age — Colorectal cancer is more likely to occur as people get older. Although the disease can occur at any age, most people who develop colorectal cancer are over the age of 50.

Polyps — Polyps are growths that protrude from the inner wall of the colon or rectum. They are relatively common in people over age 50. Most polyps are benign (noncancerous); however, experts believe that most colorectal cancers develop in certain polyps, called adenomas. Therefore, detecting and removing these growths may help prevent colorectal cancer. The procedure to remove polyps is called a polypectomy.

Familial adenomatous polyposis, or FAP, is a rare, inherited condition in which hundreds of polyps develop in the colon and rectum. Because this condition is extremely likely to lead to colorectal cancer, it is often treated with surgery to remove the colon and rectum (colectomy). Rectum-sparing surgery may be an option. Also, the FDA has approved an anti-inflammatory drug, celecoxib, for the treatment of FAP. Doctors may prescribe this drug, in addition to surveillance and surgery, to manage FAP.

Personal history — A person who has already had colorectal cancer is at an increased risk of developing colorectal cancer a second time. Also, research studies show that some women with a history of ovarian, uterine, or breast cancer have a higher-than-average chance of developing colorectal cancer.

Family history — Close relatives (parents, siblings, or children) of a person who has had colorectal cancer are somewhat more likely to develop this type of cancer themselves, especially if the family member developed the cancer at a young age. If many family members have had colorectal cancer, the chances increase even more.

Ulcerative colitis or Crohn's colitis — Ulcerative colitis is a condition that causes inflammation and sores (ulcers) in the lining of the colon. Crohn's colitis (also called Crohn's disease) causes chronic inflammation of the gastrointestinal tract, most often the small intestine (the part of the digestive tract that is located between the stomach and the large intestine). People who have ulcerative colitis or Crohn's colitis may be more likely to develop colorectal cancer than people who do not have these conditions.

Diet — Some evidence suggests that the development of colorectal cancer may be associated with a diet that is high in fat and calories and low in foods with fiber, such as whole grains, fruits, and vegetables. Researchers are exploring what role these and other dietary components play in the development of colorectal cancer.

Exercise — Some evidence suggests that a sedentary lifestyle may be associated with an increased risk of colorectal cancer. In contrast, people who exercise regularly may have a decreased risk of developing colorectal cancer.

3. What is screening, and why is it important?

Screening means checking for health problems before they cause symptoms. Screening can find polyps that may eventually become cancerous (precancerous polyps), as well as some cancers in an early stage, before they spread to other parts of the body.

Colorectal cancer screening is used to detect cancer, precancerous polyps, or other abnormal conditions. If screening detects an abnormality, diagnosis and treatment can occur promptly. In addition, finding and treating polyps may be one of the most effective ways to prevent the development of cancer altogether. Colorectal cancer is generally more treatable when it is found early.

4. What methods are used to screen people for colorectal cancer?

Health care providers may suggest one or more of the tests listed below for colorectal cancer screening.

A fecal occult blood test (FOBT) checks for hidden blood in the stool. Studies have proven that this test, when performed every 1 to 2 years in people ages 50 to 80, reduces the number of deaths due to colorectal cancer by as much as 30 percent.

A sigmoidoscopy is an examination of the rectum and lower colon using a lighted instrument called a sigmoidoscope. Sigmoidoscopy can find precancerous or cancerous growths in the rectum and lower colon. Studies suggest that regular screening with sigmoidoscopy after age 50 can reduce the number of deaths from colorectal cancer.

A colonoscopy is an examination of the rectum and entire colon using a lighted instrument called a colonoscope. Colonoscopy can find precancerous or cancerous growths throughout the colon, including the upper part of the colon, where they would be missed by sigmoidoscopy. However, it is not known whether this benefit outweighs the risks of colonoscopy, which include bleeding and puncturing of the lining of the colon. More research is needed to address these issues.

A double contrast barium enema (DCBE) is a series of x-rays of the entire colon and rectum. The x-rays are taken after the patient is given an enema with a barium solution and air is introduced into the colon. The barium and air help to outline the colon and rectum on the x-rays. Research shows that DCBE may miss small polyps.

A digital rectal exam (DRE) is often part of a routine physical examination. The health care provider inserts a lubricated, gloved finger into the rectum to feel for abnormal areas. DRE allows for examination of only the lower part of the rectum.

Scientists are still studying colorectal cancer screening methods, both alone and in combination, to determine how effective they are. Studies are also under way to clarify the risks of each test.

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