Screening for colorectal cancer

The prevalence of carcinogenesis increases along the entire gastrointestinal tract with age, driven by mucosal irritation, inflammation, impaired antioxidant mechanisms and genetically damaged epithelium.

GI cancers may cause constipation, early satiety and bleeding in the early stages — and if caught and treated early they may be cured.

Colorectal cancer screening is unique because it prevents cancer, not merely detects it. Pathy's states that regular structural examination of the colon is one of the most effective means of preventing colorectal cancer, because polyps can be found and removed before they turn malignant.

Faecal occult blood testing is rapid and easy, with a sensitivity of 82%. If positive, further diagnostic testing is recommended regardless of age.

Structural tests versus faecal tests — a key examination distinction: structural examinations are more likely to detect polyps, which can be removed, thereby preventing malignancy; faecal tests are more likely to detect malignancies early, so that treatment carries less morbidity.

Colonoscopy is the more thorough examination and is the preferred option for screening. ACS guidance quoted in Pathy's is endoscopic screening of the colon every decade over the age of 50.

Choice of test depends on extrinsic factors — transportation, availability of a gastroenterologist, the patient's willingness to undergo one procedure over another, and the patient's health status.

Screening intervals differ by test type, which is a recognised source of confusion for both patients and clinicians — clinicians must explain the strengths and limitations of each.

Textbook-supported options: FOBT or FIT-DNA every three years, or flexible sigmoidoscopy every five years, with colonoscopy preferred.

USPSTF and NCCN recommend starting at 50; ACS at 45 (textbook position).

All three recommend that screening in adults aged 76–85 be an individual decision, based on overall health and prior screening history.

USPSTF recommends against screening above 85 (grade D). In the Essentials table the grades are: A for 50–75, C for 76–85, D for >85, and I (insufficient evidence) for CT colonography and faecal DNA testing.

Pathy's also notes that most guidelines add that screening can be stopped after the age of 80.

Medicare frequencies quoted in Essentials: FOBT every 12 months; flexible sigmoidoscopy every 48 months (or 120 months after a colonoscopy); colonoscopy every 120 months (every 24 months if high risk), or 48 months after a sigmoidoscopy; barium enema every 24–48 months.

Pathy's screens by functional category: colonoscopy — "consider every 10 years" in the Robust only; FOBT — yearly in the Robust, "consider yearly" in the Frail and the moderately demented; nothing at End of life.

Primary care physicians may choose to limit screening in Frail individuals or in patients with dementia.

Colonoscopy in patients over 80 carries a greater risk of complications, adverse events and higher morbidity than in younger patients. It is also associated with a higher chance of poor bowel preparation, resulting in inadequate imaging and lower completion rates. It should be performed only after careful consideration of individual risks and benefits.

Essentials adds bluntly that the issue of risk versus benefit becomes even more relevant when procedures like colonoscopy are considered, and that most clinicians would not be enthusiastic about subjecting an 85-year-old to colonoscopy.

The "10-year rule" applies: the lag time to mortality benefit is roughly a decade, so screening is justified only when life expectancy is 10 years or more.

Screening versus diagnosis — never confuse the two. Pathy's notes that in a constipated older patient, structural examination of the colon is dictated by the need for routine screening AND by red-flag signs — rectal bleeding, anaemia, unintentional weight loss, or a recent change in bowel habit. Red flags mandate diagnostic colonoscopy at any age, irrespective of screening cut-offs.

Starting age has been lowered to 45. USPSTF (2021, still current) recommends screening from 45 to 75 years (grade B for 45–49, grade A for 50–75), with selective screening at 76–85 (grade C) based on overall health, prior screening history and patient preference. The textbook's "start at 50" is now outdated; the geriatric decision point at 76– 85 is unchanged.

Blood-based screening has arrived. On 29 July 2024 the FDA approved Guardant Health's Shield blood test for colorectal cancer screening in average-risk adults aged 45 and older — the first blood test approved as a primary screening option, meaning it can be offered like other non-invasive methods, and the first to meet Medicare coverage requirements. Approval was based on ECLIPSE, involving more than 20,000 patients, published in the New England Journal of Medicine in March 2024, showing 83% sensitivity for colorectal cancer and 90% specificity for advanced neoplasia.

But the blood test has a critical weakness for geriatric practice. Shield's sensitivity for advanced adenomas was only 13.2%, and patients with advanced adenomas are precisely those at high risk of developing colorectal cancer. The NCI notes that neither FIT nor Cologuard is as accurate as colonoscopy, and that Shield detected only 13% of advanced precancerous polyps found at colonoscopy. In other words, a blood test detects cancer but does not prevent it — it converts CRC screening from a preventive to a purely early-detection strategy. For reference, Cologuard was approved in 2014 for ages ≥50 and in 2019 for 45–49, and Epi proColon in 2016.

NordICC — the only RCT of screening colonoscopy — has now reported long-term results, and they are sobering. In the 10-year report (NEJM, 2022), the risk of colorectal cancer was 0.98% in the colonoscopy group versus 1.20% in the no-screening group, an 18% risk reduction, but colorectal cancer mortality was not significantly reduced. Uptake was only 42%; in adjusted per-protocol analysis, incidence and mortality reductions rose to 31% and 50% respectively (Gastroenterology, 2023).

The 13-year NordICC update (Lancet, May 2026 / DDW 2026) confirms the pattern. One colonoscopy significantly reduced colorectal cancer incidence but not mortality over 13 years, and colorectal cancer mortality was lower in both study groups than had been assumed when the trial was designed. The authors state that the risk of colorectal cancer death is very low even without screening, and the hope of finding a screening benefit on colorectal cancer mortality with longer follow-up is so far not substantiated. A quality caveat: as many as 30% of endoscopists in NordICC fell short of the adenoma detection rate of 25% that is the accepted quality indicator.

How this fits with the older trials. A standardised comparison found that at 10 years all randomised trials showed significant reductions in colorectal cancer incidence, but two flexible sigmoidoscopy trials and NordICC showed no significant mortality reduction, whereas PLCO saw fewer colorectal cancer deaths from year 2 (JNCI, 2025). Others argue the negative NordICC mortality result mainly reflects insufficient follow-up time, since in NORCCAP mortality differences only emerged after 9.5 years and were about four-fold greater at 12 years than at 10.

Indian position. There is no national colorectal cancer screening programme in India. The NP-NCD programme delivered through Ayushman Arogya Mandirs covers only oral, breast and cervical cancers, for ages 30– 65. CRC screening in India is therefore opportunistic, private and largely confined to symptomatic or high-risk individuals — making red-flag-driven diagnostic colonoscopy, rather than screening, the realistic pathway for most older Indian patients.