Investigations for Colorectal Cancer

Colorectal cancer can take many years to develop and early detection of colorectal cancer greatly improves the chances of a cure. The National Cancer Policy Board of the Institute of Medicine estimated in 2003 that even modest efforts to implement colorectal cancer screening methods would result in a 29 percent drop in cancer deaths in 20 years. Despite this, colorectal cancer screening rates remain low.
Your doctor will perform a physical exam and press on your belly area. The physical exam rarely shows any problems, although the doctor may feel a mass in the abdomen. A rectal exam may reveal a mass in patients with rectal cancer, but not colon cancer.
• Digital rectal exam (DRE): The doctor inserts a lubricated, gloved finger into the rectum to feel for abnormal areas. It only detects tumors large enough to be felt in the distal part of the rectum but is useful as an initial screening test. This is not painful, but it is mildly uncomfortable for some people. It takes only a few seconds.
• Fecal occult blood test (FOBT): a test for blood in the stool. Two types of tests can be used for detecting occult blood in stools i.e. guaiac based (chemical test) and immunochemical. The sensitivity of immunochemical testing is superior to that of chemical testing without an unacceptable reduction in specifity. A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, which could suggest colon cancer. However, this test is often negative in patients with colon cancer. For this reason, a FOBT must be done along with colonoscopy or sigmoidoscopy. It is also important to note that a positive FOBT doesn't necessarily mean you have cancer.
• Endoscopy:
o Sigmoidoscopy: A lighted probe (sigmoidoscope) is inserted into the rectum and lower colon to check for polyps and other abnormalities.
o Colonoscopy: A lighted probe called a colonoscope is inserted into the rectum and the entire colon to look for polyps and other abnormalities that may be caused by cancer. A colonoscopy has the advantage that if polyps are found during the procedure they can be removed immediately. Tissue can also be taken for biopsy.
• Colonoscopy is an endoscopic test. This means that a thin, flexible plastic tube with a tiny camera on the end will be inserted into your colon via your anus. As the tube is advanced further into your colon, the camera sends images of the inside of your colon to a video monitor.
• Colonoscopy is an uncomfortable test for most people. You will first be given a laxative solution to drink that will clear most of the fecal matter from your bowel. You will be allowed nothing to eat before the test. Whenever possible, you will be given medication before the procedure to relax you and relieve the discomfort.
• Flexible sigmoidoscopy is similar to colonoscopy but does not go as far into the colon. It uses a shorter endoscope to examine the rectum, sigmoid (lower) colon, and most of the left colon.

In the United States, colonoscopy or FOBT plus sigmoidoscopy are the preferred screening options.
When colon cancer is suspected, either a lower GI series (barium enema x-ray) or colonoscopy is performed to confirm the diagnosis and to localize the tumor.
A barium enema involves taking x-rays of the colon and the rectum after the patient is given an enema with a white, chalky liquid containing barium. The barium outlines the large intestines on the x-rays. Tumors and other abnormalities appear as dark shadows on the x-rays. Air-contrast barium enema is a type of x-ray that can show tumors.
• Before the x-ray is taken, a liquid is introduced into your colon and rectum via your anus. The liquid contains barium, which shows up solid on x-rays.
• This test highlights tumors and certain other abnormalities in the colon and rectum.
• Other types of contrast enemas are available.
• Air-contrast barium enema frequently detects malignant tumors, but it is not as effective in detecting small tumors or those far up in your colon.

Colonoscopy is a procedure whereby a doctor inserts a long, flexible viewing tube into the rectum for the purpose of inspecting the inside of the entire colon. Colonoscopy is generally considered more accurate than barium enema x-rays, especially in detecting small polyps. If colon polyps are found, they are usually removed through the colonoscope and sent to the pathologist. The pathologist examines the polyps under the microscope to check for cancer. While the majority of the polyps removed through the colonoscopes are benign, many are precancerous. Removal of precancerous polyps prevents the future development of colon cancer from these polyps.
If cancerous growths are found during colonoscopy, small tissue samples (biopsies) can be obtained and examined under the microscope to confirm the diagnosis. If colon cancer is confirmed by a biopsy, staging examinations are performed to determine whether the cancer has already spread to other organs. Since colorectal cancer tends to spread to the lungs and the liver, staging tests usually include chest x-rays, ultrasonography, or a CAT scan of the lungs, liver, and abdomen.
If your doctor learns that you do have colorectal cancer, more tests will be done to see if the cancer has spread. This is called staging. CT or MRI scans of the abdomen, pelvic area, chest, or brain may be used to stage the cancer. Sometimes, PET scans are also used.
Stages of colon cancer are:
• Stage 0: Very early cancer on the innermost layer of the intestine
• Stage I: Cancer is in the inner layers of the colon
• Stage II: Cancer has spread through the muscle wall of the colon
• Stage III: Cancer has spread to the lymph nodes
• Stage IV: Cancer has spread to other organs
Other screening methods
• Double contrast barium enema (DCBE): First, an overnight preparation is taken to cleanse the colon. An enema containing barium sulfate is administered, then air is insufflated into the colon, distending it. The result is a thin layer of barium over the inner lining of the colon which is visible on X-ray films. A cancer or a precancerous polyp can be detected this way. This technique can miss the (less common) flat polyp.
• Virtual colonoscopy replaces X-ray films in the double contrast barium enema (above) with a special computed tomography scan and requires special workstation software in order for the radiologist to interpret. This technique is approaching colonoscopy in sensitivity for polyps. However, any polyps found must still be removed by standard colonoscopy.
• Standard computed axial tomography is an x-ray method that can be used to determine the degree of spread of cancer, but is not sensitive enough to use for screening. Some cancers are found in CAT scans performed for other reasons.
• Blood tests: Measurement of the patient's blood for elevated levels of certain proteins can give an indication of tumor load. In particular, high levels of carcinoembryonic antigen (CEA) in the blood can indicate metastasis of adenocarcinoma. These tests are frequently false positive or false negative, and are not recommended for screening, it can be useful to assess disease recurrence. Blood tests that may be done include:
o Complete blood count (CBC) to check for anemia
o Liver function tests
o Blood tests to detect tumor markers, including carcinoembryonic antigen (CEA) and CA 19-9, may help your physician follow you after treatment.
• Genetic counseling and genetic testing for families who may have a hereditary form of colon cancer, such as hereditary nonpolyposis colorectal cancer (HNPCC) or familial adenomatous polyposis (FAP).
• Positron emission tomography (PET) is a 3-dimensional scanning technology where a radioactive sugar is injected into the patient, the sugar collects in tissues with high metabolic activity, and an image is formed by measuring the emission of radiation from the sugar. Because cancer cells often have very high metabolic rates, this can be used to differentiate benign and malignant tumors. PET is not used for screening and does not (yet) have a place in routine workup of colorectal cancer cases.
• Whole-body PET imaging is the most accurate diagnostic test for detection of recurrent colorectal cancer, and is a cost-effective way to differentiate resectable from nonresectable disease. A PET scan is indicated whenever a major management decision depends upon accurate evaluation of tumour presence and extent.
• Stool DNA testing is an emerging technology in screening for colorectal cancer. Premalignant adenomas and cancers shed DNA markers from their cells which are not degraded during the digestive process and remain stable in the stool. Capture, followed by PCR amplifies the DNA to detectable levels for assay. Clinical studies have shown a cancer detection sensitivity of 71%–91%.
• High C-Reactive Protein levels is risk marker

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