Screening of colorectal cancer identifies the tumor in the colon and rectum, resulting in cancer. The primary goal of screening is to lower the number of people who may develop the disease and reduce the number of people who die due to the condition or eliminate deaths from cancer. Colorectal cancer screening involves colonoscopy, computed tomography (CT or CAT), colonography, sigmoidoscopy, faecal occult blood test (FOBT) and faecal immunochemical test (FIT) double-contrast barium enema (DCBE), stool DNA tests. The other screening recommendations for colorectal cancer screening involve conducting colonoscopy every ten years, flexible sigmoidoscopy every five or every ten years with FIT or FOBT every year, DCBE every five years, and CT colonography more often. The tests recommended for detection of colorectal cancer involve stool DNA tests more frequently as per the doctor’s suggestion, Guaiac-based FOBT every year, and FIT every year. The screening methods for colorectal cancer should be carried out among individuals aged 45 years.
Screening Methods for Colorectal Cancer
Screening is used to check for cancer before having any signs or symptoms. Scientists have created and continue to develop tests that can screen a person for certain types of cancer before symptoms or signs appear. The goals of colorectal cancer screening are to:
- Lower the number of people who may develop the disease
- Lower the number of people who die due to the disease or eliminate deaths from cancer altogether
Screening information for colorectal cancer
Colorectal cancer can mostly be prevented through regular screening, finding polyps before becoming cancerous. Talk with the doctor about when screening should begin based on your age and family history of the disease. People with an average risk should start screening at age 45.
Talking to the doctor about the pros and cons of each screening test and knowing how often each test should be given is essential because colorectal cancer usually does not cause symptoms until the disease is advanced.
The tests for screening colorectal cancer are mentioned below 1:
- Colonoscopy – A colonoscopy helps the doctor see inside the whole rectum and colon when a patient is sedated. A flexible, lighted tube known as a colonoscope is inserted into the rectum and the entire colon to look for polyps/ cancer. A doctor can eliminate polyps or other tissue during this process for examination 2. The removal of polyps can also help in the prevention of colorectal cancer.
- Computed tomography (CT or CAT) colonography – CT colonography, sometimes called virtual colonoscopy, is a screening method being studied in some centers. It requires explanation by a skilled radiologist to provide the best results. CT colonography may be an option for people who can’t have a standard colonoscopy due to the risk of anesthesia, which is medication to block the awareness of pain, or if a person has a blockage in the colon that may prevent a complete examination.
- Sigmoidoscopy – A sigmoidoscopy uses a flexible, lighted tube inserted into the rectum and lower colon to check for polyps, cancer, and other abnormalities. A doctor can eliminate polyps or other tissue during this procedure for later examination. With this test, the doctor cannot check the upper part of the colon, the ascending and transverse colon. This screening test allows for removing polyps, which can also prevent colorectal cancer, but a colonoscopy to view the entire colon is suggested if polyps or cancer are found using this test 3.
- Faecal occult blood test (FOBT) and faecal immunochemical test (FIT) – A faecal occult blood test is used to find blood in the faeces or stool, which can be a sign of polyps or cancer. A positive test, meaning that blood is located in the faeces, can be for reasons other than a colon polyp or cancer, including bleeding in the upper GI tract or the stomach and eating rare meat or other foods. There are two types of tests – guaiac (FOBT) and immunochemical (FIT) 4,5. Polyps and cancers do not bleed continuously, so FOBT must be done on several stool samples every year and should be repeated every year. Even so, this screening test provides a reasonably small reduction in deaths from colorectal cancer, about 30% if performed yearly and 18% if done every other year.
- Double-contrast barium enema (DCBE) – For patients who can’t have a colonoscopy, an enema having barium is given, which helps make the colon and rectum look different on x-rays. A series of x-rays are then taken of the rectum and colon. Generally, most doctors would suggest other screening tests because a barium enema has fewer chances to detect precancerous polyps than a sigmoidoscopy, colonoscopy, or CT colonography.
- Stool DNA tests – This test examines the DNA from a person’s stool sample to check for cancer. It uses modifications in the DNA that occur in polyps and cancers to find out if a colonoscopy should be done 6.
Colorectal cancer screening recommendations
The American Society of Clinical Oncology (ASCO) has formed guidelines for colorectal cancer screening to prevent cancer for people with an average risk. Beginning at the age of 50, both men and women with an average risk of colorectal cancer should follow 1 of these testing schedules. People with a moderate risk do not have a family history of the disease, an inherited syndrome-like Lynch syndrome, or inflammatory bowel disease, and they have not been diagnosed with colorectal cancer in the past.
The below-mentioned tests detect both polyps and cancer:
- Colonoscopy, every ten years
- Flexible sigmoidoscopy, every five or every ten years with FIT or FOBT every year
- DCBE, every five years
- CT colonography, as often as the doctor recommends
The tests below primarily detect cancer:
- Stool DNA test, as often as the doctor recommends
- Guaiac-based FOBT, every year
- FIT, every year
Due to the increased incidence of colorectal cancer in young people, the American Cancer Society also suggests that people at average risk of colorectal cancer should start regular screening at age 45. However, this is not fully embraced yet in guidelines from other societies.
It is noteworthy that any test that indicates an abnormality should be followed up with a colonoscopy regardless of the screening and schedule.
- 1.Issa IA, Noureddine M. Colorectal cancer screening: An updated review of the available options. WJG. Published online 2017:5086. doi:10.3748/wjg.v23.i28.5086
- 2.Brenner H, Stock C, Hoffmeister M. Effect of screening sigmoidoscopy and screening colonoscopy on colorectal cancer incidence and mortality: systematic review and meta-analysis of randomised controlled trials and observational studies. BMJ. Published online April 9, 2014:g2467-g2467. doi:10.1136/bmj.g2467
- 3.Segnan N, Armaroli P, Bonelli L, et al. Once-Only Sigmoidoscopy in Colorectal Cancer Screening: Follow-up Findings of the Italian Randomized Controlled Trial–SCORE. JNCI Journal of the National Cancer Institute. Published online August 18, 2011:1310-1322. doi:10.1093/jnci/djr284
- 4.Duncan A, Turnbull D, Wilson C, et al. Behavioural and demographic predictors of adherence to three consecutive faecal occult blood test screening opportunities: a population study. BMC Public Health. Published online March 7, 2014. doi:10.1186/1471-2458-14-238
- 5.Castells A, Quintero E. Programmatic Screening for Colorectal Cancer: The COLONPREV Study. Dig Dis Sci. Published online December 10, 2014:672-680. doi:10.1007/s10620-014-3446-2
- 6.Carroll MRR, Seaman HE, Halloran SP. Tests and investigations for colorectal cancer screening. Clinical Biochemistry. Published online July 2014:921-939. doi:10.1016/j.clinbiochem.2014.04.019