Some overdiagnosis is acceptable, Brawley says. "We cure and treat some people who don't need to be treated. And in return, we save some lives." But screening has its own dangers.
Whenever you test a population, you will have some false positives. For example, if a woman is told that her mammogram is abnormal, that diagnosis might be straightened out days or weeks later, and she might find out that she does not have cancer. The diagnosis will create anxiety and lead to additional unnecessary testing.
Good health is more than absence of physical abnormality; it's also a state of mind, experts say.
"In my experience, it's not the diagnosis of cancer which really kills people," said Ezekiel Emanuel, a former oncologist, vice provost for global initiatives and chairman of the Department of Medical Ethics and Health Policy at the University of Pennsylvania. "It's the uncertainty."
The National Cancer Institute group recommended reducing the frequency of some screening examinations, focusing that screening on high-risk groups (e.g. screening smokers for lung cancer) and raising the requirements that would lead to a biopsy or other follow up care.
"We've been taught that cancer is a terrible thing and the way to deal with it always is to find it early and cut it out," Brawley said. "We're starting to realize that that is not true in all cases."