Few clinical conditions have been subject to the level of scrutiny of the effectiveness of screening as colorectal cancer. Numerous studies have shown that early detection can result in up to a 90% survival rate for stage I, but detection after the metastatic process has begun has a far worse prognosis, 11% for stage IV colon cancer.
Early cancer detection saves lives, reduces complications and reduces costs to the healthcare system and the patient. This is especially true of colorectal cancer, which the Centers for Disease Control and Prevention (CDC) describes as the third leading cause of death due to cancer in the United States. While CRC is still the third leading cause of cancer death in the United States, early detection has reduced its incidence from 79.2 cases per 100,000 in men in 1985 to 43.7 per 100,000 in men in 2013, a reduction of 45%. The incidence rate among women is lower (33/100,000 in 2013) and shows a similar decline from 57.3 cases per 100,000 in 1985. This reduction in incidence is due in the discovery and removal of precancerous polyps during diagnostic colonoscopy. However, the screening rate has plateaued at 65%.
Who recommends colorectal screening?
Early detection of cancer and detection of pre-cancerous states is a screening recommendation endorsed broadly by:
- American Cancer Society
- US Preventative Services Task Force
- American College of Gastroenterology
- American Medical Association
- Centers for Medicare and Medicaid Services
- MIPS measure #113 is colorectal cancer screening
- A variety of medical societies
While different medical societies use their own nomenclature, there are common threads involving which tests are most appropriate for detection of polyps and cancer. Stool tests (FOBT, FIT and FIT-DNA) are classified as cancer detection (American College of Gastroenterology) or “tests that find mainly cancer” (American Cancer Society) and are compared to direct visualization tests including colonoscopy, flexible sigmoidoscopy and CT/colonography which are classified as cancer prevention by American College of Gastroenterology and “tests that find polyps and cancer” by American Cancer Society.
The following table is compiled from the most recent colorectal screening recommendations for each of the tests by each organization for patients at average risk for colorectal cancer. Current data shows a lifetime risk of colorectal cancer of 4.4% in men and 4.1% in women. Each society maintains a listing of exceptions for higher risk individuals and their high-risk patient data should be referenced for this information.
US Colorectal Screening Guidelines Summary from Leading Healthcare Associations
| Screening method | Defined as | By | Frequency |
| Guaiac fecal occult blood | Stool test | USPSTF | annual |
| Guaiac fecal occult blood | Tests that find mainly cancer | American Cancer Society | annual |
| Guaiac fecal occult blood | Cancer screening test | American College of Gastroenterology | Not recommended |
| FIT | Stool test | USPSTF | annual |
| FIT | Tests that find mainly cancer | American Cancer Society | annual |
| FIT | Cancer screening test | American College of Gastroenterology | Annual |
| FIT/DNA | Stool test | USPSTF | 1 or 3 years |
| DNA | Tests that find mainly cancer | American Cancer Society | annual |
| DNA | Cancer screening test | American College of Gastroenterology | Every 3 years |
| Colonoscopy | Direct visualization test | USPSTF | Every 10 years |
| Colonoscopy | Tests that find cancer and polyps | American Cancer Society | Every 10 years |
| Colonoscopy | Tests that prevent cancer | American College of Gastroenterology | Every 10 years |
| Flexible sigmoidoscopy | Direct visualization test | USPSTF | Every 5 years |
| Flexible sigmoidoscopy | Tests that find cancer and polyps | American Cancer Society | Every 5 years |
| Flexible sigmoidoscopy | Colorectal cancer prevention | American College of Gastroenterology | Every 5-10 years |
| CT/colonography | Direct visualization | USPSTF | Every 5 years |
| CT/colonography | Tests that find polyps and cancer | American Cancer Society | Every 5 years |
| CT/colonography | Colorectal cancer prevention | American College of Gastroenterology | Every 5 years |
| mSEPT 9 DNA | Tests that prevent cancer | USPSTF | No Interval |
Colonoscopy
In the United States, colonoscopy is another screening method commonly performed to detect colorectal cancer. Done on an outpatient basis, once the patient has cleansed their colon using prescribed laxative agents, the test is performed with the patient under sedation, using a flexible tool that has a camera to visualize polyps and atypical tissue and a device to remove the tissue for examination and biopsy confirmation of whether it is cancerous or not.
Other imaging alternatives to visual methods include flexible sigmoidoscopy and CT/colonography.
Fecal Immunochemical Testing (FIT)
Around the world, beginning in the early 21st century and spearheaded by the Japanese healthcare system, newer fecal immunochemical testing methods began to be developed and introduced into the market. These tests promised a higher level of sensitivity and specificity to blood for improved screening outcomes. But, their cost per test was higher and sample collection issues persisted. Patient compliance was not substantially improved. While these tests are notably more sensitive than the guaiac methods, they are still subject to the vagaries of the disease process, including intermittent bleeding as well as lack of uniform presentation of blood throughout the stool.
Recent studies have also pointed out that the FIT tests while having a good level of sensitivity for the presence of blood from tumors are less effective at detecting polyps which are typically the first non-cancerous stage of tissue changes that lead to colorectal cancer.
The new market entrants: Changing the game?
FIT/DNA: In 2014, the FDA cleared a new test which, unlike previous tests, is performed in a reference lab setting, using the patient’s stool as a specimen. It is a combination of two different testing modalities. It uses both FIT and detection of both mutation and methylation of DNA found in the stool. The manufacturer claims the use of 11 different DNA markers in addition to detection of hemoglobin via FIT technology. A positive result is indicated by the presence of any of the DNA markers and/or hemoglobin.
In common with earlier FOBT and FIT tests, it’s a take-home test requiring the patient to perform the stool collection at home and send back to be processed at the central lab. As such, it does not avoid the compliance issues inherent in the process. It’s recommended to be performed every three years as referenced above and claims a 92% sensitivity and 87% specificity compared to FIT results.
Blood test: A new CRC Dx option
The most recently introduced screening test for colorectal cancer is a blood test. Unlike the other diagnostic tests, it stands alone in using a blood sample rather than a stool sample. The test is performed in reference laboratories and uses sophisticated real time PCR detection of methylated Septin 9 DNA which is indicative of colorectal cancer. Its sensitivity claim is ~70%% with specificity listed as ~80%.
There is a lot to know about “who to screen for what using what technology and how often” when it comes to colorectal cancer. That acknowledged, there are a few conclusions that can be made:
- The many different screening methods for colorectal cancer suit the broad range of patient conditions and preferences and are resulting in improvements in morbidity and mortality.
- Colorectal cancer screening WORKS.
- The healthcare community has developed clear guidelines regarding screening for colorectal cancer.
- The pace of technological change has advanced rapidly in the past 15 years and the healthcare community is receptive to these changes.
- New colorectal cancer markers are under development in universities and private companies and promise even better specificity in the future.
- Molecular techniques combined with blood samples rather than stool samples may pave the way for a higher level of patient compliance.