How does colorectal cancer develop?
All of the body's cells normally grow, divide, and then die in order to keep the body healthy and functioning properly. Sometimes this process gets out of control. Cells keep growing and dividing even when they are supposed to die. When the cells lining the colon and rectum multiply uncontrolled, colorectal cancer may ultimately develop.
Fortunately, most colorectal cancers begin as small precancerous (adenomatous) polyps. These polyps usually grow slowly and do not cause symptoms until they become large or cancerous. Colorectal cancer can be prevented by removing these precancerous polyps. Also, if detected early, colorectal cancer is potentially curable. That is why it is important to screen for colorectal polyps and cancer before symptoms develop.
When should screening begin?
Screening for colorectal cancer should begin at the age of 50, when the risk for developing colorectal polyps and cancer starts to increase. However, if you have a personal or a family history of colorectal polyps or cancer, screening should begin at age 40 or even younger in some circumstances. Men and women should undergo screening since colorectal polyps and cancer affect both genders.
What is involved in screening for colorectal cancer?
Several tests are used to screen for colorectal cancer. The following is a list of the most common screening tests as well as how often they should be done. Although colonoscopy the gold standard is recommended, other options are available.
- Fecal occult blood test (FOBT): This is the least accurate colorectal cancer screening test. The exam done at home checks for blood in the stool, which may be caused by large polyps or cancer. If this test is the one chosen, it should be done yearly. If blood is detected on any specimen, a colonoscopy is needed.
- Flexible sigmoidoscopy: This is a brief outpatient procedure, usually without sedation, in which the inside of the lower large intestine (the sigmoid colon and rectum) is examined using a short, flexible scope. This test should be done every five years with a yearly FOBT. If polyps are detected in the sigmoid colon or rectum, then a full colonoscopy should be performed to look for polyps in the remaining colon.
- Double contrast barium enema: This is an X-ray examination of the colon and rectum in which barium is given as an enema (through the rectum). Air is then blown into the rectum to expand the colon, producing an outline of the colon on X-ray. Barium enema is not the most accurate method and should not be the procedure of choice for colorectal cancer screening. It does require a bowel preparation. The study should be repeated every five years if no polyps are seen.
- CT colonography: In this newer method for screening, also known as CT colonoscopy or virtual colonoscopy, a CT scan of the abdomen and pelvis is performed after drinking a contrast dye and inflating air into the rectum. Like colonoscopy and barium enema, the colon must be cleaned out prior to the examination. If no polyps are seen on the CT scan, then the study may be repeated in 5 years. In the case that a polyp is found, then a colonoscopy must be performed. A CT colonography rarely identifies polyps 5mm or less in size.
- Colonoscopy: Colonoscopy is the best procedure to check for colorectal polyps and cancer. It allows for polyps to be removed during the exam. Colonoscopy is an outpatient procedure in which a physician uses a long, flexible scope to view the rectum and entire colon. This exam, performed with a light sedative, requires a bowel preparation to clean out the colon. It is usually repeated once every 10 years, unless polyps are found or there is a family history of colorectal polyps or cancer.
One of the newest methods to screen for colorectal polyps and cancer is a test that detects abnormal DNA in stool. While no one recommends that this test replace colonoscopy, it appears to be much more accurate than the fecal occult blood test:
- Fecal DNA test: The fecal DNA test works by detecting genetic mutations in the stool. Genetic material, called DNA, is present in every cell of the body, including the cells lining the colon. Normal colon cells and their genetic material are passed with the stool every day. When a colorectal cancer or a large polyp develops, abnormalities (or mutations) occur in the genetic material of the cells. Some mutations present in the polyp or cancer can be detected by laboratory analysis of the stool. This test is still considered a research tool and therefore is not a standard screening test. Because of this, the test may not be covered by insurance. The fecal DNA test is not yet widely available.
What if I have a family history of colorectal cancer?
For people with a family history of colorectal cancer, the screening recommendations are adjusted slightly to include the following:
- Begin screening at an age approximately 10 years earlier than the age at which the youngest person in your family was diagnosed with colorectal polyps or cancer. For example, if the youngest person in your family was diagnosed with colorectal cancer at age 48, you should begin screening at age 38 rather than 50.
- If you have a family history of a genetic syndrome such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC), then screening begins at a much earlier age. You should talk to your doctor about the appropriate screening interval.
- Because polyps frequently are found on the right side of the colon, screening in patients with a family history of colorectal cancer should be done with a full colonoscopy, not a flexible sigmoidoscopy.
What if I have polyps?
There are a variety of colorectal polyps, but cancer is thought to arise mainly from adenomas, the precancerous polyps. The follow-up intervals for patients with pre-cancerous polyps that have been removed include the following:
- Repeat the colonoscopy in three to five years
What are the signs of colorectal cancer?
Even if you do not have a family history of colorectal cancer or polyps, tell your doctor if you have any of the signs that could indicate a colorectal cancer, no matter what your age. Common signs of colorectal cancer include the following:
- Change in bowel habits (constipation or diarrhea)
- Rectal bleeding, especially blood on or in the stool that is either bright red or very dark
- Unusual abdominal or gas pains
- Very narrow stool
- A feeling that the bowel has not emptied completely after passing stool
- Unexplained weight loss
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 6/2/2016…#5646