The benefits of breast screening – early detection of cancer followed by rapid treatment – are finely balanced against the harms of overdiagnosis followed by unnecessary treatment and suffering, and have never been properly weighed against each other, the review by a leading epidemiologist says.
The stark conclusions mark a new phase in the war over breast screening, which has divided the medical establishment for more than 20 years. But they also raise questions about all screening programmes, including those for bowel, prostate and cervical cancers, which similarly bring harm as well as benefit.
The central drawback of screening is that in some cases the cancer (or other disease) detected does not need treating, either because it is a false alarm, because it resolves naturally or because it is very slow growing (so you die of something else). In these cases, the only result of screening is that the individual spends more of their life living in the shadow of cancer, without living longer. They may be treated, and suffer pain and anxiety, to no avail.
Supporters of the national breast screening programme, which has been running since 1988 and offers mammography (x-ray examination of the breasts) to all women aged 50 to 70 (to be extended to ages 47 to 73 by 2012), say it prevents an estimated 1,400 deaths a year. They claim that breast screening saves two women's lives for every one who receives unnecessary treatment.
Critics dispute these figures, claiming that for every woman saved, as many as 10 undergo unnecessary treatment – which can include surgical removal of the breast (mastectomy) – and up to 500 have at least one false alarm, including in up to half the cases a biopsy (the removal of a sample of breast tissue).
The simmering dispute between the two sides boiled over last March, when the British Medical Journal published a paper on breast screening in Denmark which showed that deaths from breast cancer had fallen faster in areas without screening than in those where it was used.
It concluded that the decline in the breast cancer death rate was "more likely explained by changes in risk factors and improved treatment than by screening mammography".
The paper, the latest in a series by the Nordic Cochrane Centre to be critical of breast screening, provoked a blizzard of responses accusing the researchers of "undermining the trust of women" and the BMJ of "taking sides".
Stung by the accusations, Fi Godlee, editor of the BMJ, asked Professor Klim McPherson, public health epidemiologist of Oxford University, to review the evidence, and the results are published in the BMJ's current issue.
Professor McPherson, citing US evidence, says that breast screening reduces the death rate by 14 per cent in the under-60s, which is of "marginal statistical significance", and by 32 per cent in the under-70s. But even this is a small benefit because at age 60 the risk of death from breast cancer over the next 15 years is just 1.2 per cent – 259 women in the UK would have to be screened to avoid one death.
"Individual benefit from mammography is thus very small, but this is not widely understood. In part this is due to obfuscation from organisers of mammography services assuming that a positive emphasis is needed to ensure reasonable compliance," Professor McPherson says.
He calls for a "full examination of all the data" and more honesty from the NHS about the scientific uncertainties. He also suggests that the National Institute for Clinical Excellence (NICE) should review the evidence.
"There is no doubt that screening for breast cancer has limited benefit and some possibility of harm for an individual woman and is of marginal cost-effectiveness for the community... The NHS screening programme needs to be really clear about the uncertainties when communicating with women... More importantly we all need to understand better how a national programme of such importance could exist for so long with so many unanswered questions."
Ms Godlee said: "I don't think the public understands that screening carries both risks and benefits. Often doctors don't either – they are caught up by the notion that prevention is better than cure. If you are intervening with a healthy population in the hope you can make their lives better and longer then the burden of proof is much higher and the strength of the evidence you need greater."
She added: "The screening lobby thinks the BMJ has got a bee in its bonnet about screening. That is not the case – we follow the evidence. The Danish team [from the Nordic Cochrane Centre] do good work which is very thorough and of good quality. It is fair to say that we have not had the same quality of submissions from the other side. We would be delighted if someone came forward with a robust defence of the screening programme – I don't think they have done that."
Sarah Sellars, director of the NHS Breast Screening Programme said: "The vast majority of evidence from properly conducted research clearly shows that regular mammography reduces deaths from breast cancer. The World Health Organisation's International Agency for Research on Cancer (IARC) concluded that there is a 35 per cent reduction in mortality from breast cancer among regularly screened women aged 50-69 years old.
"There is a risk of overdiagnosis, and possible subsequent overtreatment, associated with any screening programme. But recent independent studies show the risk of overdiagnosis is very much lower than some other estimates have claimed, and that the benefits far outweigh the risks."
Pink and powerful
With its pink ribbons, fashion shows, fun runs and awareness months, the breast cancer lobby is one of the most powerful health movements in the country. It has raised the profile of Britain's number one cancer, funnelled millions into research and has vigorously promoted breast screening.
But it has also sparked accusations that it has drawn attention and funds from other cancers that are "less glamorous" but cause death and illness on a greater scale. Lung cancer claims more lives but principally affects older, working class, men who lack the pulling power of the glossy young women used to front the breast cancer campaigns.
Prostate cancer charities also complain that a disease that kills almost as many men – 10,000 a year – as women who die of breast cancer – 12,000 – receives a fraction of the research income and has consequently benefited from fewer advances in treatment.
In numbers...
45,000 new cases diagnosed each year
50 per cent rise in cases in the last 25 years
12,000 deaths a year
82 per cent of patients survive for five years
66 per cent of patients survive for 20 years
50 per cent of deaths are among women aged over 70
Death rates have fallen by a third since peaking in the late 1980s
The Government needs to study the data
Editorial, Viewspaper, page 2
Comments