The problem is, we’re discovering too many cancers that don’t require action. Studies suggest that 22 to 54 percent of breast cancers found through routine mammography (and 23 to 42 percent of prostate cancers detected via prostate-specific antigen, or PSA, tests) were not fated to become life-threatening. Because it’s extremely difficult to distinguish between aggressive cancers and harmless ones during their early stages, we treat too many indolent cancers with surgery, radiation, or chemotherapy. That’s no trivial matter when these procedures can cost women their breasts or men their sexual function, not to mention the psychological toll of a diagnosis. And with the cost of treating cancer in the U.S. projected to grow as much as 39 percent from 2010 to 2020, that’s potentially billions of dollars for unnecessary action.