New bowel cancer tests some way off

Photo: A. BENOIST / BSIP via RNZ
Photo: A. BENOIST / BSIP via RNZ
It is not unusual to read articles or view television items about the exciting next big thing in cancer treatment or diagnosis.

Scratch the surface of these pronouncements, however, and we realise that there is usually still some way to go before what is being touted may reach fruition.

Recently, our attention has been drawn to research into two possible future bowel cancer detection tests, one involving dogs identifying the disease through odour in urine and the other the analysis of substances in breath.

At this stage, a dog is in training for the former, and the latter is the subject of trials.

There have already been some trials of breath-testing overseas, but it is still early days.

As Southern District Health Board’s clinical leader of gastroenterology Dr Jason Hill points out, it appears no international bowel screening programmes have introduced breath-testing yet.

What researchers are hoping is that its accuracy at detecting cancer and pre-cancerous growths would be such that only people who were considered to have these would be offered colonoscopies. In New Zealand, where we have a high rate of bowel cancer and too few colonoscopists, the attraction of this is understandable.

If the test proved really accurate, it could also be useful for symptomatic patients outside the bowel screening programme, which is currently only offered to those aged 60 to 74.

How it might work eventually is unknown. Where would the testing happen? At overworked GP clinics or special mobile clinics? Would there be equity of access concerns just as there are now?

Many will be looking forward to the results of the trials, but in the meantime, it would seem sensible to push for improvements to the current bowel screening programme that is still being introduced throughout the country.

Until the whole of the country is covered by the screening programme, we will not see its full impact on access to colonoscopy for symptomatic patients and those requiring surveillance because of their risk factors. There is already concern that there are increasing numbers of people younger than the screening age developing the disease who find it hard to receive prompt diagnosis.

Questions remain about adequacy of this programme, which picks up considerably fewer cancers than the Waitemata pilot. It used a more sensitive test and covered a wider age group — those from 50 to 74.

The ideal bowel screening programme would identify more pre-cancerous growths, resulting in higher disease prevention.

As Dr Paul Pinksy of the National Cancer Institute of Bethesda puts it: "As with cervical cancer, the ability to reduce incidence as well as mortality through minimally invasive removal of precursor lesions is a gift of nature that should be taken advantage of if at all possible."

On that theme, for years University of Otago epidemiologist and screening authority Associate Prof Brian Cox has been tirelessly advocating for offering a one-off flexible sigmoidoscopy (a procedure examining the lower bowel but requiring less bowel preparation than colonoscopy) for those aged 55.

He suggests also offering it to those aged 60 to 64 who do not want to participate in the existing screening programme which involves two-yearly testing of faeces samples for the presence of blood.

While flexible sigmoidoscopy does not pick up all cancers, Prof Cox is confident the evidence shows it would have a greater impact on reducing the number of deaths and the incidence of the disease than the existing programme.

As well as that, he says that it would save money. In a paper published last year Prof Cox and colleagues estimated it would save about $4.5million annually after 10 years of screening.

The Ministry of Health has not yet been willing to add flexible sigmoidoscopy to the national programme. The possibility of it including other diagnostic tests still under development seems a long way off indeed.


 

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