Multiple sets of guidelines support numerous tools for colorectal cancer (CRC) screening. To help clinicians determine which tools to use and how often for select individuals, Linda Rabeneck, MD, MPH, of Cancer Care Ontario, reviewed current U.S. guidelines and the supporting data backing these recommendations.
Dr. Rabeneck noted that the evidence to support CRC screening extends back 20 years and comes from several large randomized controlled trials. In brief, here is what these trials have shown:
- Routine screening with guaiac-based fecal occult blood test (FOBT) reduces CRC mortality by 15% to 33%.
- The fecal immunochemical test (FIT) appears to be superior to FOBT for the detection of CRC and advance adenomas.
- Flexible sigmoidoscopy can reduce the incidence of CRC by 21% and its mortality by 26%.
- CT colonographic screening, or virtual colonoscopy, identifies up to 90% of individuals with adenomas or cancers measuring at least 1 cm in diameter.
This body of evidence will grow in the near future as the results from several ongoing, very large randomized controlled trials mature and delineate the effectiveness of colonoscopy and stool DNA as screening tools.
Dr. Rabeneck emphasized that Western studies demonstrate that in usual clinical practice, colonoscopy is less effective for lesion detection when screening the proximal colon. In one clinical study, “the main driver of the benefit of colonoscopy appeared to be from a reduction in death from those cancers arising in the left side of the colon. Surprising results, for sure,” she commented.
Dr. Rabeneck suspects that these findings may be explained by both the quality of the colonoscopy procedure (e.g., greater difficulty cleaning and hence visualizing the right colon) and issues related to tumor biology (e.g., the presence of nonpolypoid lesions). To overcome these issues, she underscored careful attention to standard technique when using colonoscopy as a screening modality, including examining the proximal sides of flexures, folds, and valves; adequately cleaning and suctioning the colon, and performing adequate distention.
Based on much of the data cited above, in 2008 the U.S. Multi-Society Task Force issued consensus guidelines for CRC screening, with the goal of cancer prevention. These guidelines advocate routine screening for both men and women of average risk—that is, with no symptoms and family history of CRC—beginning at age 50.
To detect CRC, screening may comprise either:
- High-sensitivity FOBT or FIT every year, or
- Stool DNA testing, as often as clinically recommended.
To detect both adenomas and cancer, screening may comprise:
- Flexible sigmoidoscopy every 5 years,
- Colonoscopy every 10 years,
- Double contrast barium enema (DCBE) every 5 years, or
- CT colonography every 5 years.
Dr. Rabeneck noted that these guidelines are currently being updated and will be released in the coming months. One anticipated change is that DCBE will likely fall off the list of recommended screening tools.
The U.S. Preventive Health Services Task Force (USPSTF) also has guidelines for colon cancer screening, which are more conservative than those mentioned above. The USPSTF recommends one of the following testing methods for individuals aged 50 to 75 years of average risk:
- High-sensitivity FOBT or FIT every year,
- Flexible sigmoidoscopy every 5 years in tandem with high-sensitivity FOBT or FIT every 3 years, or
- Colonoscopy every 10 years.
At the time these recommendations were released in 2008, the USPSTF did not think there was sufficient evidence to recommend CT colonography or stool DNA testing.
The USPSTF also suggests that adults of average risk between ages 76 and 85 should not undergo routine screening because the risks outweigh the benefits. Adults older than 85 can forego CRC screening altogether.