Study finds mammograms lead to unneeded treatment

Mammograms have done surprisingly little to catch deadly breast cancers before they spread, a big U.S. study finds. At the same time, more than a million women have been treated for cancers that never would have threatened their lives, researchers estimate.

Up to one-third of breast cancers, or 50,000 to 70,000 cases a year, don't need treatment, the study suggests.