What Should Patients Know About Colorectal Cancer Screening? 

March is National Colorectal Cancer Awareness Month—an observance of patients, survivors, caregivers, and advocates to educate their communities about the disease. It is also an opportune time to promote awareness about the importance of screening, prevention, and treatment.

The third most common cancer diagnosed in the US, colorectal cancer (CRC) is one of the leading causes of morbidity and mortality worldwide. Although CRC incidence rates have declined in the U.S., disease burden remains high. About 19 million colonoscopies were done in the USA in 2017 and the number seems to be increasing primarily due to various screening programs. The U.S. Preventive Services Task Force currently recommends average-risk adults to begin screening at the age of 50 years, while the American Cancer Society suggests starting earlier, at 45 years.

Screening tests can successfully recognize precancerous polyps and can help catch early-stage colon tumors. Numerous screening options are currently available and your doctor can help you choose the right test:

Stool-based tests: 

• Guaiac Fecal occult blood test (gFOBT)
  • gFOBT analyzes the presence of blood in stool. The stool is put on guaiac saturated paper and if blood is present, a reaction occurs which causes the paper to turn blue.
  • Although this is a common screening test, it has a high incidence rate of false positives, which can occur if you have consumed red meat prior to testing

• Fecal immunochemical test (FIT)
  • FIT analyzes the presence of blood in stool but at a higher accuracy as compared to gFOBT. It identifies blood via antibodies found on the surface of red blood cells.
  • FIT does not have high false positive rates after patients consume red meat.
  • However, FIT may miss tumors that do not bleed at all and the test has to be refrigerated in order to perform accurately.

• Stool DNA test (FIT-DNA test)
  • FIT-DNA is similar to FIT but is a multi-target test that has the ability to identify small amounts of blood in stool as well as cells that have been shed in the stool.

Blood-based tests:

• Septin 9 is a blood-based test to screen for CRC.

Structural Tests:

• Flexible Sigmoidoscopy (FS)
  • Outpatient procedure
  • Patients are told to avoid food/drinks from midnight the night before
  • No sedation required
  • The time commitment required for a FS is 3-4 hours compared to a colonoscopy, which requires 48 hours

• Colonoscopy
  • Gold Standard
  • Outpatient procedure in which the patients are under sedation. A tool is inserted to visualize any abnormalities and/or polyps. A device is inserted alongside the tool to remove tissue for examinations/biopsies.
  • A few downsides to this screening test are:
    • Invasiveness of the procedure
    • Advance bowel preparation with dietary restrictions
  • Risk of tears and bleeds

• CT Colonography (Virtual Colonoscopy)
  • Minimally-invasive test to visualize the entire colon
  • High sensitivity to polyps and CRC detection
  • Alternative in patients who refuse or are unable to undergo a colonoscopy procedure

Screening for CRC should be offered to those older than 50 years as well those who have a family history of CRC and/or predisposing conditions. Patients should discuss their choice of screening test with their doctor, depending on their situation and preferences. For example, screening tests such as FIT and FS are cost-effective, yet decrease the risk of CRC.

Early detection of CRC can help improve both response to treatment and survival!