The benefits of screening for breast cancer were outlined by an Australian professor at a Wellington symposium this week, while also acknowledging the cost and anxiety it causes.
Prof David Roder, of the Cancer Council South Australia, told a National Screening Unit symposium screening programmes investigated lesions that turned out not to be cancers and led to treatment of small cancers that may not be life-threatening.
But research indicated that women who had regular breast screening by mammography reduced their chance of dying from breast cancer by about a third or more.
Deaths from breast cancer in Australia and many other western populations had dropped about 25% since 1990, Prof Roder said.
"There has been debate for some time about whether this decrease is due to better treatment or to screening offering an early diagnosis,'' he said.
It was likely a 50-50 contribution of the two factors.
In Australia there was about a 35% drop in deaths from breast cancer in a screened group of women.
There was a financial cost to screening as most women would be screened 10 times between the age of 50 and 69.
Based on South Australian data, about 20% of women undergoing screening would be called back during their 20 years of screening. Of that 20%, about 25% would ultimately be found to have a cancer.
About 20% of these cancers would be in situ cancers that were yet to invade underlying tissue.
Such lesions frequently invaded, but not always. Some might never grow, or grow so slowly they would not have been a problem.
"It has been estimated that between 7% and 8% of cancers picked up in screened women may not have progressed, although there is considerable uncertainty,'' Prof Roder said.
Research into the behaviour of in situ and other small cancers was very difficult.
"What woman with a suspected cancer is going to bide her time, for research purposes, without treatment, possibly for several years, to see what happens?''.
