Colorectal Cancer Screening
Introduction to Colorectal Cancer & Screening Methods

Colorectal cancers in their early stages have no symptoms. The great majority arise as small 3-5 mm polyps and then slowly grow into a tumor. As the colon is a capacious organ, it can distend to accommodate a large mass and still has minimal symptoms. By the time there are symptoms like pain and obstruction, the cancer is in its advance stage and cure becomes difficult.

As the best chance for complete cure is when the cancer is small and have not spread elsewhere, health authorities worldwide have advocated early detection in order to achieve complete cure.

When should I go for Screening?
Low Risk Patients Healthy people with no family history of colorectal polyps or cancer. Experts recommend starting at the age of 50 for low risk patients.
Increased risk patients
  • People with a positive family history of cancer in first degree relatives. Screening should begin at 10 years prior to the age of onset of the affected family member, or age 40, whichever is earlier.
  • Patients with personal history of polyps are also at increased risk and should be screened 2-3 years after polypectomy.
High risk People with rare genetic colorectal conditions like Familial Adenomatous Polyposis(FAP) or Hereditary nonpolyposis colorectal cancer (HNPCC). Patients with inflammatory bowel diseases are also at high risk.

Screening begins early in life and they should consult the relevant specialists on the schedule of screening and follow up.

Methods of Screening

This tests whether there is blood in the stool. It is easily available and costs very little. The disadvantage is that it is not specific as to the actual source and location of the bleed. Also, if positive a proper screening tool like colonoscopy has to be ordered either way.

CEA is a tumor marker that is closely associated with colorectal cancer. However it is not specific and can be raised in other benign conditions like inflammatory lungs and also in smokers. It can also remain normal in early colorectal cancer. As such it is not recommended as a screening tool.

This involves pumping a contrast dye into the colon and taking a series of X rays. It is considered outdated and has little indications today.

This involves passing a soft flexible fiberoptic telescope into the rectum and colon. It is very accurate and precise, and even small lesions like a 3 mm polyp can be detected and removed. In skilled hands, it can be completed in 15-20 minutes under light sedation with very low risk of complications.

Most patients sleep throughout the procedure. It is a day procedure which means patient can be discharged after the colonoscopy. Prior to the procedure the patient needs to be fasted and consume laxatives to clear the colon, but most patients tolerate this very well. Colonoscopy is the most accurate screening modality and is currently considered the gold standard in early cancer detection.

This involves using CT scan to image the entire colon and then using a sophisticated computer software to reconstruct the entire colon in 3D to screen for suspicious lesions. It involves a large amount of radiation, and can mistake stools for polyps.

Also, if a polyp is correctly identified, a colonoscopy needs to be ordered anyway. It is currently still not recommended as first line in early cancer detection, and is only indicated in patients who are unable to tolerate a colonoscopy, e.g. very elderly patients and those who have undergone multiple abdominal surgeries.