The surgery has other less common complications. In South Korea and the United States about 10 percent of patients have problems with calcium metabolism and about 2 percent experience vocal cord paralysis. And, as with any surgery, there can be life-threatening effects — blood clots in the lungs, heart attacks and strokes. In about two of every 1,000 thyroid cancer operations, the patient dies. It’s rare, but it happens.

Could what happened in South Korea happen here? Absolutely. Even without a concerted effort to promote screening, thyroid cancer incidence in the United States is up threefold since 1975. To reverse this trend, we need to actively discourage early thyroid cancer detection.

The virtue of early detection is so ingrained and so appealing that many assume that screening can only be good for you. But that’s not true. The Korean experience illustrates the downside of trying to find cancer early: overdiagnosis and overtreatment. The problem is greatest for thyroid and prostate cancer, but also exists for cancers of the lung, breast, skin and kidney. And then there is all the angst surrounding screening — that can’t be good for anyone’s health.

Of course, screening makes sense in some situations: in particular for people who are at a genuinely high risk for the cancer — those with multiple cancer deaths in their family history. People at average risk who expect to live long enough to experience the potential benefit in the future — and who are willing to accept the chance of harm from unneeded treatment now — may also decide that the screening makes sense for them.

Nevertheless, those interested in early detection may want to concern themselves with the question of how early. Sure, we would rather diagnose cancer in a small breast lump than wait until it develops into a large breast mass. But it may be excessive to extrapolate from that to searching for microscopic cancers. Many of the thyroid cancers found in South Korea were less than a centimeter in size. If we look for earlier cancers, we will always find more. And, at some point, we identify too many things that are better off left unfound. In short, having doctors not look too hard for early cancer is in your interest.

That’s where epidemiology comes in. Too many epidemiologists concern themselves not with controlling infectious disease, but with hoping to find small health effects of environmental exposures — or worse, uncertain effects of minor genetic alterations. Perhaps they should instead monitor the more important risk to human health: epidemics of medical care.