Exams and Tests

Appropriate colorectal screening leading to the detection and removal of precancerous growths is the only way to prevent this disease. Screening tests for rectal cancer include the following:

• Fecal occult blood test (FOBT): Early rectal cancer may damage blood vessels of the rectal lining and cause small amounts of blood to leak into the feces. The stool appearance may not change. The fecal occult blood test requires placing a small amount of stool on a special paper that is provided by a doctor. The doctor then applies a chemical to that paper to see if blood is present in the stool sample.
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• Endoscopy: During endoscopy, a doctor inserts a flexible tube with a camera at the end (called an endoscope) through the anus and into the rectum and colon. During this procedure, the doctor can see and remove abnormalities on the inner lining of the colon and rectum.

If rectal cancer is suspected, the tumor can be physically detected through either digital rectal examination (DRE) or endoscopy.  

• A digital rectal examination is performed by a doctor using a lubricated gloved finger inserted through the anus to feel the cancer on the rectal wall. Not all rectal cancers can be felt this way, and detection is dependent on how far the tumor is from the anus. If an abnormality is detected by a digital rectal examination, then an endoscopy is performed for further evaluation of the cancer.
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• Flexible sigmoidoscopy is the insertion of a flexible tube with a camera on the end (called an endoscope) through the anus and into the rectum. An endoscope allows a doctor to see the entire rectum, including the lining of the rectal wall. 
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• Rigid sigmoidoscopy is the insertion of a rigid optical scope inserted through the anus and into the rectum. Rigid sigmoidoscopy is usually performed by either a gastroenterologist or a surgeon. The advantage of rigid sigmoidoscopy is that a more exact measurement of the tumor's distance from the anus can be obtained, which may be relevant if surgery is required.
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• A colonoscopy may be performed. For a colonoscopy, a flexible endoscope is inserted through the anus and into the rectum and colon. A colonoscopy allows a doctor to see abnormalities in the entire colon, including the rectum.

Because the depth of the cancer's growth into the rectal wall is important in determining treatment, an endoscopic ultrasound (EUS) may be performed during endoscopy. An endoscopic ultrasound uses an ultrasound probe at the tip of an endoscope that allows a doctor to see how deeply the cancer has penetrated. In addition, a doctor can measure the size of the lymph nodes around the rectum during an endoscopic ultrasound. Based on the size of the lymph nodes, a good prediction can be made as to whether the cancer has spread to the lymph nodes.
 
Once an abnormality is seen with endoscopy, a biopsy specimen is obtained using the endoscope and sent to a pathologist. The pathologist can confirm that the abnormality is a cancer and needs treatment. A person may experience small amounts of bleeding after a biopsy is performed. If this bleeding is heavy or lasts longer than a few days, a doctor should be notified immediately.
 
A chest x-ray and a CT scan of the abdomen and pelvis are most likely performed to see whether the cancer has spread further than the rectum or surrounding lymph nodes.
 
Routine blood studies are performed to assess how a person might tolerate the upcoming treatment. 

In addition, a blood test called CEA (carcinoembryonic antigen) is obtained. The CEA is often produced by colorectal cancers and can be a useful gauge of how the treatment is working. After the treatment, the doctor may regularly check the CEA level as one indicator of whether the cancer has returned. However, checking the CEA level is not an absolute test for colorectal cancers, and other conditions may cause a rise in the CEA level. Likewise, a normal CEA level is not a guarantee that the cancer is no longer present.