Early detection has long been seen as a powerful weapon in the battle against cancer. But some experts now see it as double-edged sword.

While it's clear that early-stage cancers are more treatable than late-stage ones, some leading cancer experts say that zealous screening and advanced diagnostic tools are finding ever-smaller abnormalities in prostate, breast, thyroid and other tissues. Many are being labeled cancer or precancer and treated aggressively, even though they may never have caused harm.

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