Changes in bowel habits

In a population of 5,660 primary care patients presenting with lower bowel symptoms in one Scottish NHS Board, 4,072 were referred to secondary care. Among 1,447 who completed colonoscopy, 296 (20.5%) had significant bowel disease including colorectal cancer and advanced adenoma. While most patients with lower bowel symptoms did not have SBD (1,151 of 1,447, 79.5%), the study demonstrated that symptom-based presentation combined with faecal haemoglobin testing detected 85.1% of SBD cases at f-Hb ≥10 μg threshold. Notably, in the non-referred group B (n=2,521), 15 patients were subsequently found to have SBD upon later investigation, indicating that persistent symptoms merit follow-up even with initially negative screening.

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Among 30,893 FIT-screened participants using an 80 µg Hb/g cut-off, the interval cancer proportion was 50.8% (48.4% for men, 53.3% for women). These interval cancers were diagnosed at more advanced stages than screen-detected cancers, with 46.7% at Dukes' C and 33.3% at Dukes' D. The CRC site distribution was similar between interval and screen-detected cancers. With 19.4% of interval cancers showing undetectable faecal haemoglobin, even substantially lowering the screening threshold would not eliminate missed cancers, underscoring the importance of symptom awareness between screening rounds.

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Interval cancers accounted for 47.5% of all colorectal cancers in the screened population (502 out of 1,057 cancers among participants), indicating the guaiac faecal occult blood test has approximately 50% sensitivity. Interval cancers presented at more advanced stages than screen-detected cancers, with only 18.7% at Dukes' A stage compared to 33.9% for screen-detected cancers. Sensitivity was lower in women than men, with screening preferentially detecting cancers in males (64.7% of SCs were male vs. 52.8% of interval cancers). Screening may also be less effective for rectal cancer specifically.

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Of 755 symptomatic primary care patients completing colonic investigation, 103 (13.6%) had significant bowel disease including colorectal cancer, higher-risk adenoma, or IBD. Patients ranged from age 16 to 90 (median 64, IQR 52–73). The study demonstrated that among patients referred from primary care with bowel symptoms, a meaningful proportion had serious underlying pathology. Undetectable faecal haemoglobin provided 100% negative predictive value for colorectal cancer and 97.8% for higher-risk adenoma, confirming that symptomatic patients with bowel changes require evaluation to distinguish benign from significant disease.

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In a population-based cohort of 30,480 screening participants followed over four rounds from 2000 to 2010 with 30-month follow-up, 74 interval cancers were diagnosed after negative fecal occult blood test results compared to 97 screen-detected cancers. Interval cancers increased from 32.4% to 46.0% across the four screening rounds. Interval cancers were significantly more likely to present at advanced stages (P = 0.025) and were disproportionately located in the rectum (OR: 3.66; 95% CI: 1.51-8.88). An additional 17 cancers (18.3%) were found after inconclusive results, highlighting that negative screening does not rule out colorectal cancer.

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A mathematical model of England's population aged 30+ over a lifetime horizon estimated that a colorectal cancer awareness campaign promoting recognition of signs/symptoms and self-presentation to a GP would prevent 66 CRC deaths and gain 404 quality-adjusted life-years (QALYs). The campaign produced a 1-month 10% increase in GP presentation rates at a total cost of £5.5 million, yielding an incremental cost-effectiveness ratio of £13,496 per QALY compared to no campaign. Results were sensitive to disease stage at diagnosis, confirming that earlier presentation shifts stage distribution toward more treatable disease.

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Screening colonoscopy in 2,210 consecutive average-risk adults identified neoplastic lesions in 617 patients (27.9%), including 11 invasive cancers. Advanced proximal neoplasms were present in 1.3% of patients without any distal adenoma. Notably, 39% of advanced proximal neoplasms had no associated distal polyps, meaning these lesions would be missed by screening strategies relying solely on distal findings. Older age and male gender were independent risk factors on multivariate analysis, highlighting the need for vigilance regarding bowel symptom changes in these populations.

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