Colorectal Cancer Screening

There has reduced deaths from colorectal tumor due to colorectal tumor screening which results in early cancer detection, early cancer treatment and eventually a better outcome and higher survival rate. All individuals have different risks of developing colon cancer ranging from average risk, increased risk to high risk. Depending on your risk, different screening modalities are recommended.

Now let’s discuss about the screening tests available currently:

1.    Faecal Occult Blood Test (FOBT)
  • These tests are designed to detect presence of minute amounts of blood in the stool
  • Guaic FOBT (gFOBT) is less sensitive test as it relies on the detection of peroxidase in human blood as well as those in red meat, vegetable and some fruits. 3 specimens on consecutive days is needed
  • Faecal Immunochemical Test (FIT) is a newer and more specific test as it detects human globin which is more specific for human blood. 2 Specimens on 2 separate days are needed.
  • Whenever the FOBT is positive, a diagnostic colonoscopy is necessary to rule out any cancer

2.    Colonoscopy:
  • This is the gold standard for diagnosis as it allows direct visualization of the bowel and allows biopsy and removal of polyps at the same time.
  • Procedure requires bowel clearance prior to colonoscopy. During procedure sedation can be given to reduce discomfort.
  • Risk of perforation of bowel is (0.03-0.17%) and risk of bleeding is (0.03-0.09%).
3.    Flexible Sigmoidoscopy:
  • It is an endoscopic procedure that examines only the lower half of the colon.
  • As 2/3 of colorectal tumors are reachable with sigmoidoscope, it is rather effective.
  • It has lower risk of perforation and bleeding.
  • The main limitation is that it is unable to examine the proximal half of the colon
  • Combined FOBT and flexible Sigmoidoscopy confer better detection rates than if the modalities are used alone.
4.    CT Colonograghy (Virtual Colonoscopy):
  • This is CT images of the colon hence it is not an invasive procedure.
  • It is more superior to barium enema and is useful when actual colonoscopy is incomplete or contraindicated.
  • The only risk is cumulative radiation exposure.
5.    Double Contrast Barium Enema
  • This is a radiographic procedure which visualize colon by via instillation of barium and also distension of colon with air through a catheter inserted into the rectum
  • Before the procedure, colon preparation with dietary and laxative regime is necessary.
  • This is not the first line screening test for individuals with no symptoms.
  • It can be considered as second line of investigation if normal colonoscopy is contraindicated.

6.    Stool DNA Test
  • This detects known mutations that occur during the formation of colon cancer.
  • However currently there is lack of standardized laboratory protocols, lack of data on appropriate intervals between negative stool DNA examination and also the high costs involved hence it is not recommended for screening individuals for cancer as yet.

7.    Genetic Testing
  • Individuals and families with high risks genetic syndromes like Familial Adenomatous Polyposis and Hereditary NonPolyposis Colorectal Cancer should be referred for genetic testing.

8.    Carcinoembryonic Antigen (CEA tumor marker)
  • Not recommended as general screening in patients with no symptoms
  • It can be falsely elevated in other cancerous conditions as well as in conditions like ulcerative colitis, liver cirrhosis and also among smokers.
  • It is used mainly in patients with known colorectal tumors to monitor for persistence or recurrence of disease. 
Risk Categorization for Colorectal Tumors

Average risk individuals

This include individuals who has no symptoms and no family history of colorectal tumor

  • Your lifetime risk of developing colorectal cancer is about 5%. 
  • Grade A recommendation :  Annual Faecal Occult Blood test from age 50
  • Grade B Recommendation: Colonoscopy at every 10 years interval from age 50
  • Grade C Recommendation: CT Colonograghy at every 5 years interval from age 50

Increased risk individuals

Individuals with personal history of colorectal tumor or those who have one or more 1st degree relatives with colorectal tumor or those with prior endometrial, breast or ovarian cancer or those with previous pelvis radiation. 

  • Risk of developing colorectal cancer is slightly higher than those with average risk
  • Individuals with 1st degree relative age 60 or younger who has colorectal cancer or those who have 2 or more 1st degree relatives with colorectal cancer should have a colonoscopy at interval of every 5 years at 10 years prior to youngest case in the family or at age 40
  • Individuals with 1st degree relatives with colorectal cancer diagnosed after 60 years should have a colonoscopy at interval of every 10 years at 10 years prior to the youngest in the family or at age 50
  • Individuals with personal history of colorectal polyps should have colonoscopy 3 years after removal of polyps if the polyps have high risk features (> 1 cm, multiple polyps or villous architecture). If polyps are low risk polyps, colonoscopy should be repeated 5 years after removal of polyps.
  • Individuals with personal history of colorectal cancer should have a colonoscopy 1 year after surgery and then every 3 yearly.
  • Individuals with personal history of ovarian/endometrial (uterine) cancer should have colonoscopy one year after surgery. 

High Risk Individuals


These include people with hereditary or genetic predisposition to colorectal tumor (FAP and HNPCC) and also those with longstanding inflammatory bowel disease.

  • Those with family history of familial adenomatous polyposis should have genetic counseling and testing. They should have annual flexible sigmoidoscopy starting 10-12 years from puberty. If there are adenoma polyps present then they should have annual colonoscopy instead.
  • Those with family history of Hereditary NonPolyposis Colorectal Cancer (HNPCC) should undergo genetic testing and counseling. Colonoscopy should start from age 20-25 years at least every 1-2 years.
  • Those with inflammatory bowel disease involving the left side colon should have colonoscopy every 1-2 years starting from 15th year of diagnosis onwards.
  • Those with inflammatory disease involving the whole colon should have colonoscopy every 12 years starting from 8th year of diagnosis onwards.
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