A single colon cancer screening procedure, performed one time in midlife, may provide meaningful protection against colorectal cancer for more than two decades, according to one of the longest and largest randomized screening trials ever conducted.
The study, published May 12, 2026, in Annals of Internal Medicine, enrolled 100,210 adults between the ages of 50 and 64 in Norway and followed them for 23 years. Men who received a single flexible sigmoidoscopy were 28 percent less likely to develop colorectal cancer and 37 percent less likely to die from it compared to men who received no screening — sustained effects measured more than two decades after that one appointment.
For Americans who have been putting off colorectal cancer screening, the implication is direct: even one procedure, one afternoon, can make a significant difference.
Why This Matters
Colorectal cancer is the third most common cancer and the second-leading cause of cancer death in the United States. More than 150,000 Americans will be diagnosed this year, and approximately 53,000 will die. When caught early, colorectal cancer is highly treatable — five-year survival rates exceed 90 percent for localized disease. When diagnosed at a late stage, survival drops to roughly 15 percent.
Despite the availability of multiple effective screening tests, colorectal cancer screening rates in the United States remain below recommended levels. Colonoscopy — the gold-standard test — is effective but requires full bowel preparation, sedation, a day off work, and someone to drive the patient home. These barriers are real, and they keep many otherwise eligible people from being screened at all.
Sigmoidoscopy offers a less intensive alternative. It requires minimal preparation, no sedation, and can be performed in a standard outpatient clinic setting. The NORCCAP trial now shows that this lower-intensity option can deliver protection lasting more than two decades from a single procedure.
What We Know So Far
The NORCCAP (Norwegian Colorectal Cancer Prevention) trial is the largest and longest randomized trial of sigmoidoscopy screening ever completed. Researchers from the Cancer Registry of Norway and the University of Oslo randomly assigned 100,210 adults aged 50 to 64 to either a once-only sigmoidoscopy (with or without a stool-based fecal immunochemical test) or no screening. All participants were followed through national cancer registries until December 31, 2023 — a median follow-up of more than 23 years.
Key findings in men:
- 28 percent reduction in colorectal cancer incidence
- 37 percent reduction in colorectal cancer death
- 23-year cumulative risk of colorectal cancer fell from 6.0 percent to 4.3 percent
- 23-year cumulative risk of colorectal cancer death fell from 2.2 percent to 1.4 percent
For women, the findings were more modest. Women in the sigmoidoscopy group showed a risk reduction in colorectal cancer incidence but a minimal reduction in mortality. Researchers suggested this may relate to the fact that sigmoidoscopy examines the lower colon and rectum, and women develop proportionally more cancers in the proximal (upper) colon, which sigmoidoscopy cannot visualize.
Participants with any positive screening result — a polyp 10 mm or larger, any adenoma, or a positive stool test — were referred for colonoscopy, with 96 percent compliance.
Why This Is Particularly Important for People Avoiding Colonoscopy
The NORCCAP results are most relevant for one specific group: adults who are eligible for colorectal cancer screening but have not been screened — because they find colonoscopy too burdensome, too expensive, or too uncomfortable to pursue.
Previous meta-analyses of four large randomized trials had already established that sigmoidoscopy screening reduces colorectal cancer incidence and death for 15 years. The NORCCAP trial extends that window to 23 years, suggesting that for many people, one screening in their early 50s may provide meaningful protection through their 70s.
The trial's senior researchers noted that this "potentially reducing the need for repeated examinations within the usual screening age range" for people who receive a negative sigmoidoscopy. However, people with positive findings — who are referred for colonoscopy — and people at elevated risk due to family history or personal history of polyps should follow standard surveillance intervals.
Sigmoidoscopy vs. Colonoscopy: Understanding the Difference
| Feature | Flexible Sigmoidoscopy | Colonoscopy |
| Portion of colon examined | Lower third (sigmoid colon and rectum) | Entire colon |
| Preparation required | Minimal (enemas, no full bowel prep) | Full bowel preparation (clear liquid diet, laxatives) |
| Sedation | Typically not required | Typically required |
| Time off work | Usually same day | Usually a day or more |
| Cancer detection | Highly effective for left-sided cancers; less so for right-sided | Comprehensive |
| Insurance coverage | Generally covered | Generally covered |
Sigmoidoscopy does not see the entire colon, so it will miss cancers that develop in the right (proximal) colon. For people with a family history of right-sided colon cancer, or for those of average risk who want comprehensive screening, colonoscopy remains the preferred option.
But for people who will otherwise not be screened at all, the NORCCAP data make clear that sigmoidoscopy is substantially better than no screening.
What Doctors and Experts Say
Gastroenterologists reviewing the NORCCAP data have noted that the 23-year duration of protection is longer than previously documented and that the findings strengthen the case for sigmoidoscopy as a recommended option for adults who face barriers to colonoscopy.
As Medscape reported, the study confirms that once-only sigmoidoscopy screening in Norway reduced 23-year cumulative colorectal cancer risk in men meaningfully, representing thousands of cancers and hundreds of deaths prevented across a large population from a single mass screening.
The gender difference in benefit is an important clinical nuance. Women considering sigmoidoscopy as their primary screening method should discuss the relative merits with their physician, who may recommend colonoscopy to ensure right-sided lesions are not missed.
What the Evidence Shows — and What It Does Not
MedicalDaily Evidence Check
- Study type: Randomized controlled trial (NORCCAP — Norwegian Colorectal Cancer Prevention trial)
- Participants: 100,210 adults aged 50–64 in Oslo and Telemark County, Norway
- Published in: Annals of Internal Medicine, May 12, 2026
- Follow-up: 23 years (median), through December 31, 2023
- What it found: 28% reduction in colorectal cancer incidence and 37% reduction in mortality in men; more modest benefit in women
- What it did not prove: Equal benefit for women; benefit from sigmoidoscopy when proximal (right-sided) colon cancers are a concern; whether more frequent sigmoidoscopy would provide additional benefit
- What it does not replace: Colonoscopy for people at elevated risk, those with family history, or those seeking comprehensive examination
Who Should Consider This Finding Most Seriously
This finding is most directly relevant to:
- Adults aged 45 to 75 who have not yet completed any colorectal cancer screening
- Adults who have repeatedly delayed colonoscopy due to the preparation, recovery, cost, or time requirements
- Adults without a physician, who can now be screened at a primary care or community health center setting without requiring a gastroenterologist referral or sedation
What You Can Do Now
- If you are between 45 and 75 and have never been screened for colorectal cancer, call your primary care provider and ask about your options, including sigmoidoscopy, colonoscopy, and stool-based tests.
- If you have been avoiding colonoscopy specifically, ask your doctor whether sigmoidoscopy is an appropriate and available option for you.
- The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults aged 45 to 75. If you are in this range and unscreened, this is a conversation to have in your next primary care visit.
- If you have a family history of colorectal cancer or polyps, talk to your physician about whether a colonoscopy or an accelerated screening schedule is appropriate.
Cost and Access: What Patients Should Know
Colorectal cancer screening, including sigmoidoscopy and colonoscopy, is covered at no out-of-pocket cost under the ACA's preventive services mandate for most insured patients. For uninsured or underinsured adults, federally qualified health centers can provide referrals to low-cost or free screening programs. The CDC's Colorectal Cancer Control Program (CRCCP) funds screening programs in states and localities with low screening rates.
What Happens Next
The NORCCAP trial results have been published and are now part of the evidence base that informs global colorectal cancer screening guidelines. Additional follow-up of the NORCCAP cohort is planned. Researchers are also studying whether the benefit observed in men at 23 years will eventually materialize for women at longer follow-up. MedicalDaily will report on any guideline updates that incorporate these findings.
The Bottom Line
A 23-year randomized trial of 100,000 adults confirms what shorter-term studies suggested: a single sigmoidoscopy in midlife provides substantial, durable protection against colorectal cancer in men — lasting more than two decades from one afternoon appointment. For the millions of Americans who have delayed colonoscopy due to cost, logistics, or reluctance, this study makes clear that a less intensive alternative can still meaningfully reduce their risk. Unscreened adults between 45 and 75 should talk to their doctor about a sigmoidoscopy now.
References
- Annals of Internal Medicine — Twenty-Three–Year Benefits of Sigmoidoscopy Screening for Colorectal Cancer: A Randomized Trial (May 12, 2026)
- Medical Xpress — Single Screening Sigmoidoscopy Linked to Lower Colorectal Cancer Risk Two Decades Later
- Medscape — Sigmoidoscopy Cuts Colorectal Cancer Risk in Men
- EurekAlert — Single Screening Sigmoidoscopy Linked to Lower Colorectal Cancer Risk Two Decades Later
- The Epoch Times — Single Sigmoidoscopy Cuts Colorectal Cancer Risk for More Than 20 Years
