Researchers in Norway estimate that as many as one-quarter of breast cancers found by routine mammograms wouldn't have caused problems, but these tumors are being treated anyway.
    
The problem is there's no certain way to determine which ones are going to be life-threatening.
    
The research appears in Tuesday's issue of the Annals of Internal Medicine.
    
An editorial in the journal says breast cancer is probably overdiagnosed more in the United States. American women get screened at an early age and more often than women in Norway.
    
The researchers and other experts say women need to be better informed about overdiagnosis before they decide whether to get a routine mammogram.