One in three breast cancer patients identified through public screening programs are treated unnecessarily, a new study says.

Karsten Jorgensen and Peter Gotzsche of the Nordic Cochrane Centre in Copenhagen looked at breast cancer trends from seven years bafore and after government-run screening programs for breast cancer started in parts of Australia, Britain, Canada, Norway and Sweden.

The study found that once screening programs began, more cases of breast cancer were picked up. If a screening program was working, there should also be a drop in the number of advanced cancer cases detected in older women, since their cancers should've theoretically been caught earlier when they were screened.

However, the researchers found the national breast cancer screening systems - which usually test women aged between 50 and 69 - simply reported thousands more cases than previously identified. Jorgensen and Gotzsche found that one third of the women identified didn't actually need to be treated.

This is because some cancers never cause symptoms or death, and grow too slowly to ever affect patients. Since it's impossible to differentiate between non-harmful ones and deadly ones, any identified cancer is treated. However, the treatments can have harmful side-effects, physically and psychologically.

"This information needs to get to women so they can make an informed choice," Jorgensen said. "There is a significant harm in making women cancer patients without good reason." Jorgensen noted that for years, women have been urged to undergo screening and treatment if a cancer was identified - even if the cancer might never threaten their health.

Doctors and patients have long debated over the issue of prostate cancer screening with similar concerns that it might overdiagnose patients. A study in Netherlands found that two out of five men who were screened and found to have prostate cancer, turned out to be too slow-growing to ever be a threat.

Experts say overtreatment occurs whereever there is widespread screening. Britain's national health system recently stopped distributing pamphlets inviting women to get screened for breast cancer, after critics complained it didn't explain the overtreatment problem.

Laura Bell of Cancer Research UK said Britain's breast cancer screening program did help to reduce the country's breast cancer cases. "We still urge women to go for screening when invited," she said, also acknowledging it is crucial for women to be aware of the potential benefits and harms of screening.

[via TheHuffingtonPost]