Review puts merits of breast cancer screening under the microscope

September 2nd,2010    by Ann

The success of the national breast screening programme which offers tests to almost two million women a year has been called into question by a review which says it is harming almost as many women as it helps and must be urgently re-evaluated.

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.

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