Ann Intern Med
One sigmoidoscopy proves protective against colon cancer
Clinical Takeaway: A single sigmoidoscopy may offer durable colorectal cancer protection well beyond the standard five-year screening interval, particularly in men.
Colonoscopy has largely replaced sigmoidoscopy in colorectal cancer screening, despite being more invasive, more resource-intensive, and requiring full bowel prep. Sigmoidoscopy is a brief endoscopic exam of the rectum and lower colon, typically performed without sedation and requiring only limited bowel preparation, unlike colonoscopy.
In a 23-year follow-up of the only truly population-based sigmoidoscopy screening trial now suggests a single, less-burdensome exam can deliver durable protection, particularly for men. The benefit was larger and more consistent in men than in women.
Among men, sigmoidoscopy was linked to a 28% reduction in colorectal cancer incidence and a 37% reduction in colorectal cancer death. Among women, incidence dropped by 11%, with no statistically significant reduction in death. The mortality benefit in men was driven largely by reduced deaths from distal cancers and from metastatic disease, which fell 33% in men but only 5% in women.
A secondary signal pointed to long-term protection from polyp removal rather than early detection alone. Yearly hazard ratios in men showed two distinct dips in cancer death, one at two to five years (consistent with early detection) and a second at nine to 12 years (likely reflecting the cancer-preventing effect of polypectomy). That pattern suggests a single sigmoidoscopy may continue to protect for more than a decade after the procedure.
The NORCCAP trial randomized 98,654 Norwegians aged 50 to 64 between 1999 and 2001 to either one-time sigmoidoscopy screening (with or without a fecal immunochemical test) or no screening, with follow-up through national cancer and death registries. Screening adherence was 61% in men and 65% in women. Adding fecal blood testing to sigmoidoscopy did not improve outcomes beyond sigmoidoscopy alone.
The sex disparity remains incompletely explained. The authors note that women had higher rates of proximal colon cancer, which sigmoidoscopy cannot reach, and that men more often had distal lesions detected at screening that triggered follow-up colonoscopy. Differences in education, income, ethnicity, marital status, and occupation did not account for the gap. Endoscopy quality measures were similar between sexes.
The American Cancer Society and US Preventive Services Task Force recommend starting screening at age 45 for average-risk adults, with sigmoidoscopy every five years or colonoscopy every 10 years among the accepted options.
The data also offer a reminder that sigmoidoscopy remains the only colorectal cancer screening modality with a randomized signal for reducing all-cause mortality, even as colonoscopy has displaced it in most settings.
"A single flexible sigmoidoscopy can have a long-lasting effect on CRC incidence and death," the authors concluded. "In this 23-year follow-up of a truly population-based, once-only sigmoidoscopy screening trial, there was a sustained benefit in CRC incidence reduction for men and women, but statistically significant reduction in CRC death was seen only for men."
Source: Botteri E. Ann Intern Med. 2026 May 12. Twenty-Three-Year Benefits of Sigmoidoscopy Screening for Colorectal Cancer: A Randomized Trial