There’s no question that colon cancer screening saves lives.
But the preferred screening method – colonoscopy or the less invasive and less costly sigmoidoscopy – remains an area of uncertainty. Colonoscopy should, intuitively, perform better. After all, the scope travels beyond the reach of the sigmoidoscopy, allowing a doctor to inspect the proximal intestine for any lesions that, if left unchecked, could transform into life-threating malignancy. However, to date, no large-scale randomized trial has compared the two head-to-head, and thus guidelines do not recommend one method over another.
In the setting of this uncertainty, Reiko Nishihara and colleagues offer a significant contribution with their original article, “Long-Term Colorectal Cancer Incidence and Mortality after Lower Endoscopy,” published in this week’s NEJM
With the goal to determine the relative role of colonoscopy and sigmoidoscopy in protection against colon cancer, specifically cancers in the proximal colon, authors enrolled nearly 89,000 patients whom they followed for 22 years. Twice yearly from 1988 to 2010, patients were surveyed and reported whether they’d received a colonoscopy or sigmoidoscopy. what was found, and whether they had received a diagnosis of colon cancer.
Their findings: Those who underwent colonoscopy had a lower incidence of cancer in the proximal and distal colon, whereas the study participants screened by sigmoidoscopy saw a decreased incidence only of distal cancer. Furthermore, patients who underwent colonoscopy were less likely to die from proximal colon cancer.
Based on their findings, the authors concluded that if all the patients had undergone colonoscopy, an additional 40% of colorectal cancers, including 61% of distal cancers and 22% of proximal cancers, might have been prevented.
Additionally, authors explored the duration of protection afforded by a negative colonoscopy. Their findings support the current recommendations for colonoscopy every 10 years in low-risk, or more frequently in high-risk patients.
Finally, the authors used their population to examine whether there are distinct characteristics of colon cancer that presents less than five years after a negative colonoscopy. They found that –yes – these cancers are associated with specific molecular features. Of note, they might be more commonly predated by sessile serrated lesions, which are potentially harder to see or to remove effectively – raising the question of whether any of these particularly aggressive forms of colon cancer could be prevented with improved colonoscopic technique.
The authors do not go so far as to recommend colonoscopy over sigmoidoscopy, in light of their findings, nor does an accompanying editorial. However, as physicians await randomized trials comparing the methods of colon cancer testing, these findings offer useful data to bring to our clinical practice.
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