How is bowel cancer missed during a colonoscopy in Ireland?

A colonoscopy lets a doctor look directly at the lining of the bowel using a flexible camera. It is the test most likely to find bowel cancer and to remove the growths, called polyps, that can turn into cancer over time. When it is done well, it is very effective. When it is done poorly, the protection it should provide can fail.

Why a colonoscopy can miss a cancer

A cancer can be missed for several reasons. The scope may not reach the full length of the bowel, leaving the right side unexamined. The bowel may be poorly cleaned out, so debris hides the lining. The doctor may withdraw the camera too quickly to inspect properly. Flat growths on the right side of the colon are pale and easy to overlook, and they can be missed if the inspection is rushed.³ A cancer can also be seen but recorded incorrectly, or a polyp can be removed and then not followed up.

The pattern of missed cancers is not random. They are found more often on the right side of the colon, in the caecum and the ascending colon, than on the left. Part of the reason is a type of growth called a sessile serrated lesion, which sits flat against the bowel wall rather than standing out like a typical polyp.³ These are harder to see, easier to hide behind a poorly prepared bowel, and reaching them depends on the scope being passed to the caecum. That is why completeness and inspection quality matter so much.

How often does a colonoscopy miss cancer?

It helps to put the numbers in context. According to the HSE National Screening Service, the BowelScreen post-colonoscopy cancer rate in Ireland is 4.3 percent.¹ Internationally, research published in the journal Medicine estimates that around one in five pre-cancerous growths is missed at colonoscopy. That figure rises to between a third and a half of flat lesions, and higher again when the bowel is poorly prepared.¹⁵ These figures are not proof of fault in any single case. They show why an examination that meets the recognised standards matters, and why one that does not can leave a cancer to grow.

This page focuses on the examination itself as the point of failure. If your cancer was missed because a GP ignored your symptoms or did not refer you, that is a different claim. It is covered on our failure to refer for investigation page. If the colonoscopy was done correctly but a removed sample was misread in the laboratory, that belongs with pathology and laboratory errors. For the wider picture across the cluster, see our guide to bowel cancer misdiagnosis claims.

What makes a colonoscopy negligent under Irish standards?

A missed cancer is not automatically a negligent one. Colonoscopy has an accepted miss rate, and the law does not expect perfection. The question is whether your examination met the quality standards a reasonably competent colonoscopist would have met. Those standards are written down, and they can be measured against your records.

The National Screening Service publishes the Standards for Quality Assurance in Colorectal Screening, now in its third edition.² These set out what a complete and adequate examination looks like. They are not vague guidance. They give measurable targets that an expert can check against your colonoscopy report. Where a procedure clearly falls short of them, that shortfall becomes objective evidence of a breach under the test the Irish courts apply.⁵

It is worth being clear about jurisdiction here. These are Irish standards set for Irish endoscopy units, and the breach is judged by Irish law. Much of the material online about missed colonoscopies describes the UK system, with its own screening ages and its two-week-wait referral rule. That framing does not apply to a claim in Ireland, where the pathway runs through the National Cancer Control Programme and BowelScreen.

The standards that matter most when a cancer is missed are set out below. A single failure does not prove a claim on its own, but a pattern of them, recorded in your own notes, is often where a case begins.

What do these colonoscopy terms mean?

A few technical terms come up repeatedly in these claims. Knowing what each one means helps you read your own colonoscopy report and understand where an examination may have fallen short.

Post-colonoscopy colorectal cancer (PCCRC)

A bowel cancer diagnosed within 36 months of a colonoscopy that was reported as clear, or after a polyp was removed. In Ireland the BowelScreen rate is 4.3 percent.¹

Interval cancer

A bowel cancer found within 36 months of a negative screening colonoscopy. It is the screening-programme version of a post-colonoscopy cancer, and a proportion of these are unavoidable.¹

Caecal intubation rate (CIR)

The proportion of colonoscopies in which the scope reaches the caecum, the start of the large bowel. The recognised standard is at least 90 percent, with 95 percent the aspirational target, confirmed by a photograph.²

Adenoma detection rate (ADR)

The proportion of colonoscopies in which at least one pre-cancerous growth is found. It is a recognised measure of how carefully the bowel lining is inspected, and a consistently low rate is linked to missed cancers.⁶

Sessile serrated lesion

A flat, pale growth found more often on the right side of the colon. Because it sits flat against the bowel wall, it is harder to see than a typical raised polyp and is missed more often.³

Is it an interval cancer or a negligent missed cancer?

Two terms matter here, and the difference between them often decides a case. A post-colonoscopy colorectal cancer is a bowel cancer diagnosed within 36 months of a colonoscopy that was reported as clear, or after a polyp was removed.¹ An interval cancer is the same idea within a screening programme. These cancers happen in every bowel screening programme in the world, and a proportion of them are genuinely unavoidable.

BowelScreen has measured its own rate. For every 100 people diagnosed with bowel cancer after a BowelScreen colonoscopy, about 4.3 were post-colonoscopy cancers. The National Cancer Registry Ireland confirmed that figure, and it sits inside the accepted international range of 2.5% to 8.5%.¹ That rate is reported as a sign the programme is working to standard, not as proof of fault.

The legal claim arises when expert review shows your cancer was not one of the unavoidable ones. If a tumour was there to be seen, or the examination fell short of the standards above, the cancer was probably missed rather than genuinely new. That is the difference between a tragic but blameless outcome and a negligent one, and it is decided by an independent expert reading your records, not by the rate alone.

There is a recognised way of doing this. When a post-colonoscopy cancer is reviewed, it is classified by its most likely explanation. This separates a lesion that was probably missed or removed incompletely from one that genuinely arose later.¹ An expert applies that same logic to your case. Where the most plausible explanation is a missed lesion on a colonoscopy that did not meet the standard, the claim has a foundation. Where the cancer was genuinely new and the examination was sound, it does not.

The Wexford General Hospital colonoscopy recall

Ireland already has a documented example of what systemic colonoscopy failure looks like. Between March 2013 and November 2014, concerns were raised about the quality of colonoscopies carried out by one consultant at Wexford General Hospital.⁷ The service there was run on behalf of the national BowelScreen programme.

After two patients were found to have cancers following recent colonoscopies, a review began. In total, 615 colonoscopies were re-examined and 401 patients were recalled for a repeat procedure.⁷ An internal review identified 13 probable missed cancers. One of those patients had died before the review, and the case was linked to at least one avoidable death.⁸

An external review by Professor Robert Steele of the University of Dundee examined how the case was handled. It found the health service had missed early opportunities to act on a staff member's concerns about the colonoscopist.⁸ The episode shows two things that matter for a claim. A run of missed cancers can come back to a single examiner whose work fell below standard, and the evidence often sits in reviews the hospital itself has carried out.

How do you prove negligence after a "clear" colonoscopy?

An Irish medical negligence claim has two parts, and both must be proved. The first is breach of duty. The second is causation, meaning the breach actually caused harm. A missed cancer on its own satisfies neither.

Breach is judged by the test from Dunne v National Maternity Hospital.⁵ The question is whether the colonoscopist did something no colonoscopist of equal standing, acting with ordinary care, would have done. This is where the quality standards do their work. An expert gastroenterologist compares your report against them. They check whether the caecum was reached and photographed, how the bowel preparation was recorded, how long the withdrawal took, and whether a poor examination was repeated. The same expert compares the original report against the tumour found later. The size and site of that cancer often show whether it should have been visible at the time. To understand how this standard is applied in practice, see our explanation of how breach of duty is proved.

Causation is often the harder part. The defence will argue the cancer itself caused the harm, not the delay. Under the ordinary "but for" test, you must show that but for the missed diagnosis the outcome would have been better. Where a delay let a curable early tumour grow into a later-stage one needing far more aggressive treatment, that argument can be met.

Irish law also recognises the loss of a chance. Even where earlier treatment might not have cured the cancer, a patient deprived of the chance to be treated sooner may still have a compensable claim. This area is not fully settled, because the Supreme Court has decided cases that pull in different directions.⁹ Our page on the loss of chance doctrine explains where the law currently stands and why expert evidence on timing and staging is so important.

Does a screening or symptomatic colonoscopy change your claim?

Where your colonoscopy came from can affect the claim. A screening colonoscopy follows a positive home test under BowelScreen, which invites people aged 57 to 71 and refers about one in twenty for a colonoscopy after an abnormal result.¹⁰ A symptomatic colonoscopy is one your GP or a consultant arranged because you had symptoms such as bleeding or a change in bowel habit.

The standards of competence are the same for both. The difference is who carries the legal duty. In organised screening, the Supreme Court in Morrissey v HSE confirmed that the health service owes a non-delegable duty to participants. It cannot escape responsibility by pointing to a contractor.¹¹ That can shape who a claim is brought against and how it is run. For most claimants the practical effect is the same, because the focus stays on whether the examination met the standard.

Timing is measured against two different Irish benchmarks. After a positive home test, BowelScreen expects a screening colonoscopy within 20 working days.¹⁰ For a symptomatic patient referred with red flags such as bleeding or weight loss, the HSE target is an urgent colonoscopy within 28 days. The stated target is zero breaches.¹³ Those targets are under strain. The Irish Medical Times, reporting HSE National Scorecard data, found that 6,660 patients waited longer than four weeks for an urgent colonoscopy in 2025. That was an increase of nearly 84 percent on the year before, with some patients waiting up to 60 days.¹⁴ A delay against these benchmarks can form part of a claim where it allowed a cancer to advance.

What evidence in your colonoscopy report matters?

A claim of this kind is built from documents, and most of them already exist. You are entitled to your medical records, and you can ask the hospital or BowelScreen for the full file. Our guide on following up abnormal results covers how requests and recall failures are documented.

When reviewing whether a colonoscopy was adequate, an expert looks for a short list of objective markers in the report.

• The completeness statement, confirming whether the caecum was reached, with a photograph of the caecal landmarks.
• The bowel preparation score, showing how well the bowel was cleaned and whether a poor prep was repeated.
• The withdrawal time, showing how long the lining was actually inspected.
• Any polyps found, their size and location, and whether removal was complete.
• The histology from your later diagnosis, to compare the tumour with what the original report described.

A report missing a completeness statement or caecal photographs, recording a poor preparation without a repeat, or noting a rushed withdrawal, shows the red flags an expert examines first.

What can a bowel cancer claim include?

Compensation in Ireland falls into two parts. General damages cover the pain, suffering and reduced quality of life caused by the avoidable progression of the cancer. These are assessed under the Personal Injuries Guidelines, which replaced the older Book of Quantum in 2021, and any figure depends entirely on the facts of the individual case.¹² We do not publish award estimates, because doing so would be misleading and is not permitted.

Special damages cover financial loss that can be calculated. In a missed bowel cancer case these are often substantial. They can include loss of earnings, the cost of more extensive surgery and chemotherapy, the lifelong cost of stoma care, and home adaptations after major surgery. Unlike general damages, special damages are not capped. A clinical negligence claim of this kind does not go through the Injuries Resolution Board, which assesses standard injury claims but not medical negligence. It proceeds through the High Court.⁴

Time limits and the date of knowledge

The deadline for a medical negligence claim in Ireland is two years less one day.⁴ In a missed cancer case the important point is when that clock starts. It usually runs from your date of knowledge, not the date of the procedure. That is when you first knew, or could reasonably have known, that the earlier colonoscopy may have been at fault. Our page on the date of knowledge in cancer claims explains how this is worked out.

Because the date of knowledge depends on the facts, the safest step is to get advice early. Waiting risks the deadline passing before the link between the missed colonoscopy and your diagnosis becomes clear.

What should you do if you think your colonoscopy missed cancer?

If you had a colonoscopy and were later diagnosed with bowel cancer, a few practical steps protect your position while you decide whether to make a claim.

1. Request your full colonoscopy record in writing, including the report, the bowel preparation score, the withdrawal time, and any photographs or video.
2. Keep the histology and staging from your later diagnosis, so the cancer found can be compared with the original report.
3. Ask a solicitor to arrange an independent review of the colonoscopy by an expert gastroenterologist.
4. Check the time limit early, because it usually runs from your date of knowledge rather than the date of the procedure.

How we can help

Common questions

References

1. Health Service Executive, National Screening Service. Measuring our rate of post-colonoscopy bowel cancers (accessed June 2026).
2. National Screening Service. Standards for Quality Assurance in Colorectal Screening, Third Edition (2023, accessed June 2026).
3. PMC. Circumstances in which colonoscopy misses cancer (accessed June 2026).
4. Irish Statute Book. Civil Liability and Courts Act 2004, s.7 (two-year limitation period), and Statute of Limitations (Amendment) Act 1991 (date of knowledge) (accessed June 2026).
5. Dunne v National Maternity Hospital [1989] IR 91, Supreme Court of Ireland (accessed June 2026).
6. PMC. Quality in colonoscopy: national standards and key performance indicators (accessed June 2026).
7. The Irish Times. 13 cancers missed in Wexford hospital colonoscopies (2017, accessed June 2026).
8. RTE News. External review of the Wexford General Hospital missed cancers (accessed June 2026).
9. Philp v Ryan [2004] IESC 105 and Quinn v Mid-Western Health Board [2005] IESC 19, Supreme Court of Ireland (accessed June 2026).
10. Health Service Executive, National Screening Service. BowelScreen is now for everyone aged 57 to 71 (2026, accessed June 2026).
11. Morrissey v Health Service Executive [2020] IESC 6, Supreme Court of Ireland. Judgment on BAILII (accessed June 2026).
12. Judicial Council. Personal Injuries Guidelines (2021, accessed June 2026).
13. Irish Examiner. HSE National Scorecard: urgent colonoscopy 28-day target (target of zero breaches) (accessed June 2026).
14. Irish Medical Times. Stark rise in patients waiting over four weeks for urgent colonoscopies (2026, accessed June 2026).
15. Medicine (Baltimore), PMC. Risk factors of missed colorectal lesions after colonoscopy (accessed June 2026).