Japanese public health officials were aware of an increased incidence of thyroid cancer in Russian children after the 1986 Chernobyl nuclear accident. So researchers screened more than 300,000 Fukushima-area children 18 and under for thyroid irregularities that could turn into cancer.
The scientists’ initial findings set off alarms. Tests detected some 30 times more cases of early thyroid cancer in Fukushima children than in children elsewhere in Japan who weren’t exposed to the reactor radiation. Many children underwent biopsies, and some even had their thyroid glands removed, a procedure that carries risks and means a child must take thyroid pills for the rest of his or her life.
The lesson of the Fukushima children is that intensive screening will reveal more disease — but not necessarily more disease that must be treated.
This phenomenon is called overdiagnosis. Screenings find cancers that did not need to be treated because they would grow slowly, if at all. Left alone, they would probably never cause problems. But it can be difficult to distinguish between trivial abnormalities and those that ultimately cause disease.