Survival rates are higher when measured earlier
Survival rates always go up with early diagnosis: people who get a diagnosis earlier in life will live longer with their diagnosis, even if it doesn't change their time of death by one iota.
-- H. Gilbert Welch, professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice and an author of "Overdiagnosed: Making People Sick in the Pursuit of Health."
Screening proponents have also encouraged the public to believe two things that are patently untrue.
First, that every woman who has a cancer diagnosed by mammography has had her life saved (consider those "Mammograms save lives. I'm the proof" T-shirts for breast cancer survivors). The truth is, those survivors are much more likely to have been victims of overdiagnosis.
Second, that a woman who died from breast cancer "could have been saved" had her cancer been detected early. The truth is, a few breast cancers are destined to kill no matter what we do.