* There is some nuance here. Technically, you want to detect cancers as soon as possible, but you also want to know how bad the cancer will be. For example, some prostate cancers grow so slowly that a person is likely to die from natural causes long before the cancer becomes an issue. If you know the cancer isn’t going to kill you in your remaining lifespan, then you may choose to avoid the unpleasant therapy, with its risk of impotence or incontinence. Some doctors worry all this data will lead to overtreatment.