Medical Matters: Enthusiasm for cancer screening is still very high

You would be hard pressed to find a lay person who is critical of cancer-screening programmes. BreastCheck and Cervical Check are seen as life-saving interventions; witness the outcry when programmes were rolled out slowly on a regional basis or, in the case of breast cancer, do not yet cover a wider age cohort.

Public enthusiasm for cancer screening is very high, as recent research published in the British Journal of Cancer shows. A survey of almost 2,000 men and women aged from 50 to 80 across the UK, carried out by researchers at University College London (UCL), revealed that 89 per cent of them thought cancer screening for healthy people was "almost always a good idea". This was backed up by a strong belief among respondents that finding a cancer early would mean less treatment would be needed.

Despite growing evidence that cancer screening may be harmful for some, almost half of those surveyed in the UCL study said they would even wish to be screened to see if they had a slow-growing cancer that would be unlikely to cause them harm in their lifetime. In other words, the concept of harm by overdiagnosis hasn’t really hit home: in breast-cancer screening, for example, it has been calculated that for every woman whose life is saved by screening, three women will be overdiagnosed and treated for a cancer that would not otherwise have come to light or have affected their quality of life or their longevity.

Intervention

Last year a major 25-year trial, which followed just under 90,000 Canadian women aged 40 to 59 who underwent annual mammography, found the screening intervention had no impact on mortality from breast cancer. More than one-fifth of the cancers detected were overdiagnosed, representing one overdiagnosed breast cancer for every 424 women screened. It is the latest in a series of major trials questioning the “absolute” good of breast-cancer screening.

Nonetheless, some two-thirds of women in the UCL study judged a person who didn’t go for screening to be “irresponsible”, which challenges the idea of cancer screening being seen as a personal choice. Indeed, it raises a question of whether we have oversold the cancer-screening story.

And yet participation rates in programmes have dropped slightly in the UK. In the bowel-screening programme there, about half of people who get sent the home-screening kit actually return it. In Ireland, some 72 per cent of women invited to have a mammogram by BreastCheck turn up for screening.

Meanwhile, another recent study in the Lancet examined the effect of including information about the possible harm caused by overdiagnosis and overtreatment in packs given to women before they choose whether to take part in mammography screening programmes.

The Australian research found that women who received detailed explanations about the possible harms linked to screening, had “significantly less favourable attitudes towards breast-cancer screening”. And while attitudes to screening remained positive overall, fewer respondents said they intended to undergo breast-cancer screening in the future.

The information packs showed outcomes of breast screening over 20 years, compared with no screening, and included data on breast- cancer mortality reduction, over- detection and false positive diagnoses. Commenting on the results, lead researcher Prof Kirsten McCaffery of the University of Sydney said: “Momentum is shifting from uninformative and persuasive approaches to screening communication to clear and balanced information, giving people the opportunity to make informed choices based on their assessment of the trade-offs between potential outcomes.”

While we are notoriously poor at estimating risk, especially in healthcare, our actions suggest we have quite an entrenched view of cancer as an inevitable killer: we do not seem to be able to accommodate the reality that some tumours do not need treatment even when that treatment has no clear benefit and could, in itself, harm our health. Is this a case of do as I say, not as I do? mhouston@irishtimes.com muirishouston.com