Most Americans would undoubtedly agree that the best way to avoid dying from cancer — apart from not getting it in the first place — is by catching tumors as early as possible. That has been the thinking behind more than half a century of cancer treatment, and it’s the basis for such screening technologies as mammography, spiral CT scanning (used to detect lung cancer) and the P.S.A., or prostate specific antigen test, all of which are aimed at detecting tumors when they are small and most easily removed or destroyed by chemotherapy or radiation. But this year brought forth a number of studies that questioned whether early diagnosis really does much good. Early detection, some researchers now say, is probably saving few lives. More here.