A third of women diagnosed with breast cancer in public screening programmes are treated needlessly because their tumour will not be life-threatening, the British Medical Journal (BMJ) reported Friday.
A study by Scandinavian experts highlighted the dilemma facing doctors when it comes to detecting and treating breast cancer -- the notorious "silent killer" of women, thus named for the way it can stealthily claim lives.
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In some cases, the cancer will grow so slowly that the patient will die of other causes before it produces symptoms, or it may remain dormant over the years or even shrink.
Because doctors have no idea whether the cancer will be lethal or harmless, they tend to treat all patients diagnosed with a tumour. But cancer treatment, using powerful drugs, radiotherapy or surgery, causes harm.
So it is vital to know how many patients may be being treated unnecessarily, especially given the huge investment in having women undergo regular mammograms.
Karsten Jorgensen and Peter Gotzsche of the Nordic Cochrane Centre in Copenhagen pored over data from screening programmes in Australia, Britain, Canada, Norway and Sweden.
They looked at trends seven years before the programmes were implemented, and seven years after.
They found that when screening programmes were introduced, doctors did indeed spot more cases of breast cancer -- but also treated more women who would not have needed it.
"One in three breast cancers detected in a population offered organised screening is overdiagnosed," they estimated.
In an editorial also published by the BMJ, Gilbert Welch, a professor at the Dartmouth Institute for Health Policy and Clinical Research in Vermont, said the findings raised the key question about the trade-off between deaths avoided and harm inflicted by screening programmes.
One study has suggested that one death is avoided for every two women who are "overdiagnosed," while another puts the ratio far higher, at one death avoided for every 10 cases of unnecessary treatment.
Welch called on the medical profession to draw up a simple statistical table to help women weigh the risks and the benefits from breast-cancer treatment.
"Mammography undoubtedly helps some women but hurts others," said Welch. "No right answer exists, instead it is a personal choice."
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