Colon Cancer Screening

The colon and rectum are part of the large intestine, which absorbs nutrients from the digested food and stores the solid waste until it is expelled from the body.

Colon cancer screening is the process of looking for polyps and cancerous outgrowths on the inner wall of the colon and rectum when no gastrointestinal symptoms are present for the disease. A polyp is a noncancerous outgrowth that may become cancerous later. Early detection and removal of the noncancerous polyp and malignant tumours can thus prevent further complications and death due to colon cancer.

The people at high risk of colon cancer are:

• People above 50 years
• People with an inherited familial adenomatous polyposis, a condition where individuals develop numbers of polyps in colon and rectum
• People who had colon cancer earlier
• Women with a previous history of breast, ovarian or uterine cancer
• People whose close family members such as parents, siblings or children have or had colon cancer
• People with ulcerative colitis and Crohn’s disease 
•  People with sedentary lifestyle, unhealthy eating habits and who smoke

People should talk to their doctor regarding when to go for the screening and what tests to have. One or more of the following tests may be used for colon cancer screening:

Flexible Sigmoidoscopy: A sigmoidoscope is used to view the inside of the rectum and lower colon. A finger size thick tube with a camera at the end is inserted from the rectum and images of the inner wall of rectum and part of colon can be seen on the monitor. It can be used for taking a biopsy of the polyp or tumour and for removing some polyps, but a colonoscopy needs to be done to view the whole colon and remove all polyps or tumours. It is fairly safe but has a small risk of bowel tear, bleeding and infection.

Colonoscopy:  A colonoscope is similar to sigmoidoscope but is longer and is used to examine the inner wall of the whole of the colon. It is inserted from the rectum and the doctor can see images of the entire colon on the monitor. Special surgical tools can be passed through the colonoscope to take a biopsy and remove polyps. Sedation is required. There is a small risk of bowel tear, bleeding or infection after the procedure.

Virtual Colonoscopy: It is the computed tomography scan of the colon. The person is made to lie on a table of the CT scanner which takes cross-sectional images of the colon. It is a non-invasive technique and does not require sedation. If any abnormalities are found, a colonoscopy needs to be done to remove the polyps or tumours.

Double contrast Barium Enema: A small tube is inserted in the rectum and barium sulfate, a white chalky liquid, and then air is pumped into the colon. The barium suspension lines the outer walls of the colon. X-ray images of the colon are then taken to reveal abnormalities on the inner wall of the colon. If abnormalities are found, a colonoscopy is done to remove the polyps or tumours.

Faecal Test: They are done with the faecal sample and are totally safe. These may not give confirmatory results but may suggest the abnormalities in the gastrointestinal tract warranting further tests. Colonoscopy needs to be repeated if results are positive indicating the presence of a cancerous growth in colon. They are of three types:

• Faecal Occult blood test detects blood in the faeces not visible to normal eyes through chemical reaction.
• Faecal Immunochemical test detects blood through specific immunochemical reaction of a protein in the blood and can detect hidden blood.
• Stool DNA test looks for certain abnormal DNA genes in the cells shed from cancerous outgrowth or polyps in the stool sample. It is expensive as compared to the other stool test.