PARIS - 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 on 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 lies.

Not all breast cancers kill, though.

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.

Mr Karsten Jorgensen and Mr 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. -- AFP