Colon Cancer Screening — What Is Colorectal Cancer?

Colon cancer occurs in the large intestine (called the colon). Rectal cancer is found in the rectum (which is the part of the large intestine closest to the anus). These cancers have many common features and are often referred to together as colorectal cancer. They can be detected through colon cancer screening.

Colorectal cancer is the second leading cause of cancer deaths in the US. Many happen because the cancers are found too late for effective treatment. If colorectal cancer is detected early enough, it is usually very treatable and not life-threatening.

What are the signs and symptoms of colorectal cancer?

Most colorectal cancers begin as a polyp ("pohl-ip"). At first, they are small, harmless growths in the wall of the colon. However, as they grow, they can develop into a cancer that grows and spreads.

See your doctor if you have any of the following warning signs:

Rectal Bleeding
Blood in Your Stool or Toilet After a Bowel Movement
A Change in Stool Shape or Consistency (Such as Diarrhea or Constipation
Lasting Several Weeks)
Cramping in Your Lower Stomach
Discomfort or an Urge for a Bowel Movement When There is No Need for One
Weakness or Fatigue
Unintended Weight Loss

Other conditions can cause these symptoms, as well. You should see your doctor to determine the cause.

What are screening tests for colorectal cancer?

Screenings can find polyps or cancers before they cause any symptoms. Cancer screening tests are vital because early detection means it can be more effectively treated. Your doctor chooses the right tests for you. Here are some screening tests for colorectal cancer:

Fecal Occult Blood Test - This detects blood that you can't see in your stool. Your doctor gives you a test kit and instructions for home use. You return the sample to your doctor for testing. If blood is found, another test is conducted to look for a polyp, cancer, or other cause of bleeding. Your doctor will tell you to avoid certain foods or medicines that may interfere with test results for a few days before the test.

Particular foods and medicines can deliver a positive result, even though there is no blood in your stool. This is called a "false-positive" test. These foods and drugs include some raw vegetables, horseradish, red meat, non-steroidal anti-inflammatory drugs (such as ibuprofen), blood thinners, vitamin C supplements, iron supplements, and aspirin. Conditions like hemorrhoids can also cause a false-positive result.

Flexible Sigmoidoscopy - In this test, your doctor puts a thin, flexible, hollow tube with a light on the end into your rectum. The tube is connected to a tiny video camera so the doctor can look at the rectum and the lower part of your colon.

This test may be slightly uncomfortable, but it allows your doctor to see polyps when they are tiny (before they can be discovered with a fecal occult blood test). Because flexible sigmoidoscopy might overlook cancerous polyps in the upper colon, some doctors prefer a colonoscopy. Your physician will discuss the options with you.

Barium Enema - During this test, you are given an enema (injection of fluid into the rectum) with a liquid that makes your colon show up on an X-ray. Your doctor checks the X-ray to find abnormal spots in your colon. If an abnormal spot is observed or the radiologist detects polyps, your doctor will probably ask you to have a colonoscopy.

Colonoscopy - Before this test, you take a medicine that makes you relaxed and sleepy. A thin, flexible tube connected to a video camera is inserted into your rectum, so your doctor can look at your entire colon. The tube can also remove polyps and cancers during the exam. A colonoscopy may be uncomfortable, but not usually painful.

Virtual Colonoscopy - This new test uses a computerized tomography (CT) machine to capture pictures of your colon. Your physician can see the images combined in a computer to check for polyps or cancer. If polyps or abnormalities are found in your colon, you will require a traditional colonoscopy to examine the polyps more closely or remove them.

Stool DNA Test - This checks your stool for cells that are shed by colon cancers or precancerous polyps. Your doctor provides a test kit with stool sample collection instructions. Your doctor may ask you to refrain from certain foods or medicines that may interfere with test results a few days before the test. If your test is positive, your doctor will probably want you to have a colonoscopy.