Sydney, Nov 13 : Overdiagnosis of invasive breast cancer could be as high as 42 percent, says a new study.

The study shows the reduced mortality rate from increased mammography screening has a flipside.

There is 30 to 42 percent excess of women diagnosed with invasive breast cancer, over that expected, who undergo unnecessary treatment.

This translates to about 23 to 29 percent of all breast cancers diagnosed as being

overdiagnosed and over treated.

"Other studies have looked into overdiagnosis of breast cancer before but our findings are unique," says Alex Barratt, study co-author and associate professor, University of Sydney.

"They take into account risk factors such as hormone replacement therapy and obesity, both of which have increased the prevalence of breast cancer since about the same time as publicly-funded mammography screening programmes were introduced.

"Even when these risks are accounted for, we still find breast cancer overdiagnosis is very high. Overdiagnosis means many women are needlessly having surgery or other treatment at great personal cost," Barrat says.

"We know there is overdiagnosis across the population but we can't pinpoint which women are overdiagnosed," he adds, according to a Sydney varsity release.

These findings were published in the latest issue of Cancer Causes Control.(IANS)