Methods to diagnose thyroid cancer may be almost too good, according to the authors of a paper published in the New England Journal of Medicine.

Imaging such as MRIs, CTs and ultrasonography have advanced so that even incidences of disease in the thyroid that would not normally cause any kinds of symptoms or death are being detected, diagnosed and possibly unnecessarily treated.

For example, the biggest case of over-expected diagnoses came in South Korea. Between 1993 and 1997, about 12 cases were diagnosed per 100,000 people. But then between 2003 and 2007, the incidence rate jumped to nearly 60 cases per 100,000 people. Higher-than-expected incidence of diagnosis was especially prevalent in women, more than a quarter of whom between ages 50 and 59 underwent some kind of thyroid cancer-detecting imaging in those years.

And other countries have seen similar, though smaller, disparities. In the U.S. between 2003 and 2007, almost 30 per 100,000 middle-aged women were diagnosed with the cancer while the incidence rate for the same age group was fewer than 20 women per 100,000 between 1998 and 2002. In nearly all of the countries studied (South Korea, the U.S., France, England, Scotland, Japan, Italy, Australia and others), middle-aged women were diagnosed more frequently than older women, a previously unseen trend.

The study authors wrote, “We attribute the excess cases beyond the number predicted by the multistage model to diagnoses of asymptomatic disease subsequent to improved diagnostic technology and increased surveillance, predominantly in young or middle-aged populations.”

The trend especially was assisted by gynecologists offering younger and middle-aged women thyroid screening tests. About 90 percent of the over-diagnoses came from women, the researchers estimated. This rise in testing, and therefore diagnosis, in this group allowed researchers to estimate the over-diagnosis rates of the countries studied.

Between 1988 and 2007 in the U.S., there were possibly 228,000 unnecessarily diagnosed cases of thyroid cancer. In Italy: 65,000; France: 46,000; Japan: 36,000; and in South Korea: 77,000 between 1993 and 2007. In total, about 470,000 women might have been unnecessarily diagnosed with thyroid cancer in the 12 studied countries during this period.

The trend held with men as well, who might have seen 90,000 unnecessarily diagnosed cases in that time, though they were older than the women at age of diagnosis.

On the other hand, the researchers pointed out, risk factors for thyroid cancer were also on the rise during that period, such as incidence of diabetes, obesity or radiation exposure, which might explain the rise in diagnosis. But flip the perspective again, the paper’s authors pointed out, and the researchers realized that increasing levels of those risk factors might have led to increasing surveillance and therefore the increase in diagnosed cases might still be unnecessary.

Over-diagnosis could have harmful effects such as unnecessary and risky surgeries or radiation. In fact, the paper authors pointed to research showing that carefully watching and waiting for change in thyroid cancer could be just as effective as going for immediate surgery.

“The examples of South Korea, the United States, Italy, and France suggest that other countries should exercise caution against systematic screening for thyroid cancer and overtreatment of small nodules and suggest that watchful-waiting approaches should be considered a research priority and a preferable option for patients with low-risk papillary thyroid cancers,” the authors wrote.