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We also have a case study of over diagnosis from Korea:

http://www.npr.org/sections/health-shots/2017/05/09/52756929...

"South Korea is the poster child for the problem of overdiagnosis" of thyroid cancer, Welch says. About 15 years ago, doctors there started a mass campaign to screen for thyroid cancer. That vastly increased the rate of thyroid cancer, to the point that it exceeded cases of breast cancer and other common malignancies.

Yet Welch notes that the mortality rate from this cancer didn't change at all. "So all these extra cases were cases of thyroid cancer that weren't destined to bother people," he said. Instead, that rash of overdiagnosis sent people into needless surgery.

Harmless thyroid tumors are surprisingly common. Decades ago, pathologists in Finland noticed that more than a third of the people they saw in autopsy had thyroid tumors, but the cancers had no negative consequences.