London - A harvard study study of 16 million women has cast doubt on the benefits of routinely offering breast cancer screening.
The data suggests that routine screening is leading to significant numbers of “false positives” - in which women are wrongly told they might have breast cancer when, in fact, they do not.
Other women might undergo gruelling chemotherapy to treat small, slow-growing tumours which might never have troubled them if they lived on in ignorance.
Routine screening for breast cancer was introduced in Britain 25 years ago, with the hope that catching symptoms early would enable the cancer to be treated before it had spread.
In the UK, women aged 50 to 70 are invited for a mammogram every three years.
Doctors say this approach has been incredibly successful, contributing to improving the prognosis for patients, with 87 percent of British women now surviving for more than five years after a breast cancer diagnosis.
Last month a study of ten million by researchers at Queen Mary University of London found that routine breast screening cuts cancer deaths by 40 percent among middle-aged women.
In the UK, this relative risk translates to around eight deaths prevented per 1 000 women regularly attending screening.
But in recent years there has been mounting controversy over the negative impacts of screening. Some experts argue that catching a tumour early pushes women into having potentially harmful treatment such as radiotherapy and chemotherapy, in some cases unnecessarily.
There also fears that many women are wrongly told they might have cancer, leading in some cases to needless breast removal. The new study, led by doctors at Harvard University in Massachusetts, suggests that increasing the numbers of women offered routine mammograms simply increases the rate of overdiagnosis.
Their research, published in the respected medical journal JAMA Internal Medicine, compared the health records of 16 million women aged 40 and over across the US. They compared the extent to which mammograms were used in 547 US areas. The team found that in areas where mammograms were used more, the number of women told they had cancer increased.
But they found no corresponding decrease in breast cancer deaths - which would be expected if the screening was effective.
Of the records they examined, 53 207 women were diagnosed with breast cancer and followed up for ten years. In areas that used screening 10 percent more than the average, there were 16 percent more breast cancer “diagnoses” - but no significant change in breast cancer deaths.
The researchers saw a 25 percent increase in the number of small breast cancers spotted, which would be expected if the cancers were identified early.
But there was no reduction in the number of large tumours, which should have been seen if screening was effective and the cancers had been spotted before they grew.
The authors, led by Professor Richard Wilson, wrote: “What explains the data? The simplest explanation is widespread overdiagnosis, which increases the incidence of small cancers without changing mortality, and therefore matches every feature of the observed data.”
The authors advised that their findings should be treated with caution, adding that because their data was merely statistical, there was no way to draw clear conclusions about cause and effect.
Daily Mail