As part of its campaign against “too much medicine” The BMJ has published reviews that question the value of screening for breast cancer in women and aneurysm in men – asking whether the harm of “over-diagnosis” outweighs the benefit of detecting and treating real cases of disease.
In the case of breast cancer, the analysis of the history of screening for the disease, written by a public health expert, calls for “urgent agreement” in the debate and controversy that exists between scientists.
For abdominal aortic aneurysm, the review about screening men who do not have symptoms suggests that the ratio of harm to benefit of carrying out these programs has worsened over the years.
This, they say, is thanks to a reduction in risk factors such as smoking, which has reduced the chance that screening will succeed in finding actual cases.
And a third paper looks at the results of surveys that gauged the level of over-diagnosis people would accept from screening programs aiming to detect different cancers – finding a wide range of attitudes to the harm or benefit of screening.
In the research on abdominal aortic aneurysm (a swelling in the main artery from the heart, which can lead to death when it ruptures), the authors estimate that 176 of every 10,000 men invited to screening are over-diagnosed.
This means smaller aneurysms being picked up – and perhaps being repaired in preventive surgery – even though they might have swelled little and presented a low risk of rupturing.
The researchers describe the real-life consequences of the programs, which, in the UK, invite all men over the age of 65 for screening, and in the US, only those who have smoked (a risk factor that greatly increases the likelihood of an aneurysm). They explain:
“These men are unnecessarily turned into patients and may experience appreciable anxiety throughout their remaining lives.”
“Moreover,” the authors continue, “37 of these men [out of every 10,000 screened] unnecessarily have preventive surgery and 1.6 of them die as a consequence.”
In addition to such risks of psychological burden, the authors cite the surgical risks for those who undergo a preventive operation, and the public health implications over cost-effectiveness.
“When health authorities invite asymptomatic men to screening, there should be no doubt that benefits clearly outweigh harms,” the authors conclude. “We cannot judge whether this is true of abdominal aortic aneurysm screening: the harms have not been adequately investigated, as is true for cancer screening.”
On the question of how good the harm-to-benefit ratio is for breast cancer screening, Prof. Alexandra Barratt, from the School of Public Health at the University of Sydney in Australia, gives an overview of the history of screening programs, and offers a list of ways to improve their benefit.
Writing her review for The BMJ‘s “too much medicine”
- Do better research to quantify the true amount of over-diagnosis – by developing “internationally agreed standards” for studies that monitor the problem created by screening programs
- Investigate less aggressive treatment options for screen-detected breast cancers
- Be more wary of new technology – for example, digital mammography has increased cancer detection without reducing death rates, so three-dimensional mammography (tomosynthesis), which “promises a 30-50% increase in detection of breast cancers” should not be implemented without more research on “whether it alters the balance of benefit and harm”
- Provide quality information to women. “Many women continue to be ‘prescribed’ or encouraged to undergo screening rather than being supported to make an informed choice,” says Prof. Barratt, yet “information is an intervention that may have both positive and detrimental effects”
- Think twice before extending screening programs – “extending screening to women in their 70s has been shown to significantly increase the incidence of early-stage breast cancer, and this could have detrimental effects for older women.”
Prof. Barrett says lessons have been learned in breast cancer screening that should inform programs for other cancers. Breast cancer has “led the way in developing awareness” about the potential for screening to over-diagnose and treat people who have no symptoms, and this is also needed for “the early detection of lung and thyroid cancers, as well as breast and prostate cancers.”
This neatly leads to the subject of the third paper, on cancer screening more generally, which analyzes people’s risk attitudes in relation to the early detection of different cancers and varying levels of benefit.
Dr. Ann Van den Bruel – a senior clinical research fellow at the University of Oxford’s Nuffield department of primary care health sciences in the UK – conducted a survey with colleagues “to describe the level of over-detection people would find acceptable in screening for breast, prostate and bowel cancer.”
Her “striking” findings, from asking people in the UK’s general population, were that more people would accept a screening program that created over-detection “in the entire population” being tested than would accept “no over-detection at all.”
People aged 50 or older accepted less over-detection, however, and there was a wide overall variation in the risks of over-diagnosis that people would accept from cancer screening.
The average levels of “acceptability” ranged from 113 cases of over-detection in every 1,000 people screened, to 313 cases.
People were significantly less happy to accept the risk of being over-diagnosed with bowel cancer than they were of this happening with breast or prostate cancer – the latter, in other words, being more worthwhile screening for in terms of perceived benefit versus risk.
The following results from the study highlight the two extremes expressed for attitudes to screening:
- 4-7% of respondents indicated they would tolerate no amount of over-detection at all from a screening program
- 7-14% considered it would be acceptable for the entire screened population to be over-detected – that is, doing the screening would be worthwhile even if it resulted in all 1,000 people tested being unnecessarily diagnosed.
The survey asked questions about three different types of cancer screening: breast cancer for women, prostate cancer for men, and bowel cancer for both.
For each type, the researchers presented the absolute number of cases there were each year in the UK, plus a description of the treatment, including adverse effects. They then presented two scenarios of screening effectiveness: a 10% reduction in deaths from the specific cancer, or a 50% cut.
Dr. Van den Bruel says:
“People accepted more over-detection when they perceived a higher benefit from cancer screening, so from a 10% mortality reduction to 50% mortality reduction, median acceptability increased significantly, with a maximum of 313 cases per 1,000 people screened for breast cancer.”