Screening for colorectal cancer can save lives!

Screening for colorectal cancer can save lives!


Assoc. Professor, Dr. Supakorn Rojananin, M.D.

Deputy Dean of Public Relations and Special Affairs

Faculty of Medicine Siriraj Hospital, Mahidol University


            From the statistical report of Siriraj Cancer Center in the years 2000-2004, colorectal cancer ranked the fourth most common cancer in Thailand. It came the third in female after breast and cervical cancer (6.4%) and the second in male after lung cancer (9.17% of the total cancers treated). The age standardized incidence rate was 7.6 and 6.0 per 100,000 for men and women respectively.


            Colon and rectum is called large intestine or the lower part of the intestine after small bowel extending from the right abdomen, traversing to the left at the mid-abdomen below stomach and descending down along the left flank to form the rectum. . The colon is about 5 feet long and the rectum is the last six to eight inches above the anal canal. Its main function is to reabsorb water and some nutrients from food and store solid waste until it passes out the body as feces.


            Most colon and rectal cancers originate from benign wart-like growths on the mucosal layer of the bowel called polyps. However, not all polyps have the potential to transform into cancer. Those that do have the potential are called adenomas and take more than 10 years to develop into cancer. Only those with a strong family history of colorectal cancer or adenoma and in persons with some colonic diseases, such as ulcerative colitis or Crohn’s colitis may develop faster, but the incidence is not common. The average age to develop cancer is 70 years, and 93% of cases occur in persons 50 years of age and older.


            Men tend to get colorectal cancer at an earlier age than women, but women live longer so they catch up with men and thus the total number of cases in both sexes is relatively equal.


            Symptoms of colorectal cancer vary depending on the location and the extent of the cancer. The most common presenting symptom is rectal bleeding. In the late stages of the left sided colon cancer may also cause constipation, abdominal pain, and obstructive symptoms. On the other hand, the right sided colon cancers may produce vague abdominal aching or mass but are unlikely to present with obstruction or altered bowel habit due to the still liquidity of the feces on the right side. Other symptoms may include weakness, weight loss, or anemia resulting from chronic blood loss.


            According to Associate Professor, Dr. Narong Lert-akayamanee, Division of General Surgery, Department of Surgery, most patients came to seek medication when they already had symptoms which sometimes were too late or the tumors were too large. The tumor may be invading to lymph nodes, bloodstream, or spreading to nearby organs such as liver which was incurable by mean of surgery alone. On the contrary, the cancer is highly curable when it is small or localized to the bowel or asymptomatic with an 80 to 90 % chance of survival for 10 years.


            The precancerous polyps usually show no symptom and become increasingly common with age. By age 50, 10% has polyps, but by the age 65 that number grows to 30%. If untreated, 8 to 12 % of the polyps will become cancerous.


             Dr Narong urges, therefore, that colorectal cancer screening should be encouraged in general population beginning at the age of 50. If screening detects an abnormality, diagnosis and treatment can occur promptly. Even though we do not know the exact causes of the cancer, but if it is found early it is generally more treatable.


            The screening programs include; fecal occult blood test.  This simple test is used to find hidden blood in the feces when early cancer usually release small amount of blood from damaged vessels. If this test is positive, a colonoscopy is needed to see if there is a cancer, polyps or other causes such as hemorrhoids, diverticulosis, colitis, etc. This test is recommended yearly after 50.


            Barium enema with air contrast or double-contrast barium enema was once a procedure of choice for screening in 5 year interval by putting the barium sulfate (chalky substance) and air to the entire colon through the anus. This test will give the x-ray pictures of the lining of the colon. If abnormality is found, colonoscopy should be followed. Due to the high false negativity of the procedure, the test is rarely performed recently.


            Colonoscopy is an examination of the entire colon, rectum under sedating medicine by using a slender, flexible lighted instrument to view inside of the bowel. The scope can be connected to a video camera and display monitor for a better view. If any abnormality is found, the tissue can be removed in total or biopsied for pathology. Bowel preparation is required for both barium enema and colonoscopy one day before the procedure. If there is no abnormality, this test is recommended every 10 years.


            Flexible sigmoidoscopy is also another option for detection of any abnormality within lower colon and rectum not more than 2 feet from the anal canal.


            Virtual colonoscopy is a new technology of x-ray of the colon and rectum. After bowel preparation, air is pumped into the colon to distend it. Then spiral CT scan is done and animation of the entire colonic lumen was made in a 3 D picture. This is probably more accurate than the barium enema but not quite as good as colonoscopy for finding very small polyps.


            The appropriate screening program for individuals should be discussed with your family physicians in detail.  For those with an increased risk, screening should be done earlier and more often than recommended.