Routine bowel cancer screening 'does more harm than good'

However, an international panel of experts say that this protocol "may have little or no effect on cancer incidence over 15 years".

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Writing in the British Medical Journal (BMJ), they say that screening should be restricted to individuals with an above average risk of developing colorectal cancer.

A typical adult who reaches 50 in Europe or North America has a 1-2 per cent chance of developing the disease over the next 15 years.

The researchers said routine screening should apply to people aged 50 to 79 with a risk score of 3% and above, based on factors such as family history, ethnicity, smoking, alcohol intake, diabetes and BMI, because this was the threshold at which the balance of benefits to harms tilted in favour of screening.

Harms included false positives and infections or injuries from unnecessary procedures.

Those individuals should be given a choice of four different screening options, they said, including an annual or biannual FIT test, a colonoscopy, or a sigmoidoscopy.

They recommended using a UK-devised risk scoring system called the QCancer model, and stressed that those with a particularly elevated risk due to a previous bowel cancer or because they have conditions such as inflammatory bowel disease or Lynch Syndrome, should be subject to a separate, more rigorous screening regime.

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A record number of people in Scotland are taking part in bowel screening, with an increase in the number of 'positive' tests being returned - from 1.9% using the old Faecal Occult Blood Testing (FOBT) test kit to 3.1% under FIT, which was introduced in November 2017.

However, fewer than one in 10 'positive' screening tests turn out to be cancer, leading to fears that screening could put undue pressure on diagnostic services such as colonoscopy. One in three patients currently wait longer than the six-week target time.

Epidemiologist Professor Philippe Autier, of the Strathclyde Institute for Global Public Health, said prioritising higher risk individuals "is likely to optimise overall screening effectiveness while reducing overdiagnosis".

He said: "Health professionals under time constraints can decide to focus on high risk individuals for conversations about screening.

"We [also] know from randomised trials and observational studies that eligible people who don't participate in screening programmes are at higher risk of death from colorectal cancer.

"A risk based approach may work particularly well for people who would otherwise remain refractory to screening."

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Dr Lisa Wilde, director of research at Bowel Cancer UK, said they would welcome a risk-based approach in future, but did not believe this was possible at present.

She said: “Inviting people to take part in bowel cancer screening based on their individual risk of developing the disease is absolutely something we would like to see in the future.

"However, at the moment we’re a long way off this being possible and as the research highlights, there is more work needed in this area to make this a reality.

“We know that the current bowel cancer screening programme saves lives.

"The new screening test, the Faecal Immunochemical Test, is a game changer as it can detect twice as many cancers and four times as many adenomas than the previous screening test and is much easier for people to use.”

A Scottish Government spokeswoman said: "Any successful screening programme must balance the detection of the disease being screened for with acceptability and safety of the test being used.  Screening and early detection is crucial to improving cancer survival.

"Urgent cancer referrals are always fast tracked and the Scottish Referral Guidelines for Suspected Cancer were recently refreshed, providing specific guidance on how to handle high risk symptoms.

“The Scottish Bowel Screening Programme follows UK National Screening Committee advice and invites men and women aged between 50 and 74 to take part in screening every two years.

"This recommendation is based on evidence about the effectiveness and benefits of screening people in this age range.

"Colonoscopy is offered in cases where FIT highlights a heightened risk of bowel cancer.”