Colon cancer screening using colonoscopy has significantly decreased the incidence and mortality of colorectal cancer in the United States. In the National Polyp Study (NPS), colorectal cancer was prevented by removal of adenomatous polyps.1 A more recent study looking at long-term follow-up from the NPS demonstrated a 53% reduction in colon cancer mortality with colonoscopy and polypectomy.2
Current screening guidelines recommend identification of those with inherited cancer syndromes with distinct screening/management recommendations, and for all others options including fecal occult blood testing yearly, flexible sigmoidoscopy, computed tomography colonography, barium enema, and colonoscopy beginning at age 50. Those individuals with low-risk adenomas (one or two adenomas < 10 mm) are advised to undergo surveillance colonoscopy every 5 to 10 years, whereas those with high-risk adenomas (high-grade dysplasia, villous adenoma, tubular adenoma ≥ 10 mm, or more than three adenomas) are evaluated every 3 to 5 years.
Study Details
As summarized in this issue of The ASCO Post, Løberg and colleagues report their data from over 40,000 patients in Norway from a large database study assessing the long-term risk of colorectal cancer after adenoma removal.3 Colorectal cancer mortality was estimated in this cohort using the linked Cancer Registry and Death Registry of Norway. The study demonstrated a lower risk of colorectal cancer mortality with “low-risk” adenomas than with those considered “high risk.” Higher risk was defined as having multiple adenomas or adenomas with villous histology and/or high-grade dysplasia. While this definition does not take into account polyp size, it still allows for a reasonable level of risk stratification. The median follow-up was 7.7 years.
Colonoscopy every 10 years remains the gold standard strategy for colorectal cancer screening, although there are other options as mentioned above.4 These latter options are not as effective for cancer screening and do not allow for therapeutic intervention if a polyp is identified. More recently, stool DNA analysis (fecal immunochemical test) has demonstrated promise with improved accuracy, but further data are still needed to validate this option for colorectal cancer screening.
Implications and Limitations
The major goal and impact of screening is identification and removal of adenomatous polyps. It is clear that patients who develop adenomas remain at risk for future development of polyps and as such warrant colonoscopic surveillance after polyp removal. With this knowledge, the Norwegian study has significant impact on our understanding of colon polyps and cancer development. The data could significantly alter surveillance intervals for patients with low-risk adenomas, as it appears they have very low risk of interval malignancy. The data may further drive gastroenterologists to ensure high-risk adenomas are completely resected or undergo more-advanced endoscopic mucosal resection to ensure this is the case. The implications of extending surveillance intervals for low-risk patients not only would result in significant cost savings but would potentially increase patient compliance for follow-up.
There are some potential limitations of this data set. We need to keep in mind there is an environmental and racial component in colon carcinogenesis. It is quite possible that these and other factors may be different in the Eastern world compared to the United States, for example, and could influence the age at which screening should commence and the interval between screening assessment. Furthermore, while 7.7 years median follow-up is significant, the data would be that much more meaningful with observation beyond 10 years.
Moreover, Norwegian guidelines do not recommend surveillance colonoscopy for adenomas before 10 years. This is significantly different from the 3 to 5 year follow up performed in the United States. Dr. David Lieberman’s editorial accompanying the report by Løberg and colleagues also emphasizes that the quality of colonoscopy is an important factor, particularly for high-risk patients, since it is known that missed lesions on initial colonoscopy can account for development of future colorectal cancers, as can incomplete removal of polyps.5
In summary, the work by Løberg and colleagues is an excellent cohort study and advances our understanding of the progression of colon carcinogenesis. It is possible these data may have a significant effect on resource allocation in gastroenterology. That being said, the current study does not demonstrate that aggressive colonoscopic surveillance is justified, but rather suggests that there may be a role for risk stratification based on adenoma detection.
As such, care should be taken when extrapolating the data to all populations across the world. Further prospective studies are needed to validate surveillance intervals and strategies for high- and low- risk adenomas. In the meantime, patients and clinicians should routinely discuss the quality of the colonoscopy, the determination of high- vs low-risk adenomas, and the risks vs benefits of a future surveillance strategy. ■
Disclosure: Drs. Komanduri and Benson reported no potential conflicts of interest.
References
1. Winawer SJ, Zauber AG, Ho MN, et al: Prevention of colorectal cancer by colonoscopic polypectomy. The National Polyp Study Workgroup. N Engl J Med 329:1977-1981, 1993.
2. Zauber AG, Winawer SJ, O’Brien MJ, et al: Colonoscopic polypectomy and long-term prevention of colorectal-cancer deaths. N Engl J Med 366:687-696, 2012.
3. Løberg M, Kalager M, Holme O, et al: Long-term colorectal-cancer mortality after adenoma removal. N Engl J Med 371:799-807, 2014.
4. Lieberman DA, Williams JL, Holub JL, et al: Colonoscopy utilization and outcomes 2000 to 2011. Gastrointest Endosc 80:133-143, 2014.
5. Lieberman DA: Colon-polyp surveillance—Do patients benefit? N Engl J Med 371:860-861, 2014.
Dr. Komanduri is Director, Interventional Endoscopy, Division of Gastroenterology and Hepatology, Feinberg School of Medicine, Northwestern University, and Dr. Benson is Professor of Medicine, Division of Hematology-Oncology, Department of Medicine, and Associate Director for Clinical Investigations, Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago.
