12 minors were diagnosed with thyroid cancer and 15 others suspected cases, according to the findings of an ongoing study on the impact of radiation on residents after the Fukushima atomic power plant disaster.
The number of confirmed cases is up from three in a report in February, and other suspected report is up from seven.
The figures were taken from about 174,000 people aged 18 or younger whose initial thyroid screening results have been confirmed.
According to the Japan Times, researchers at Fukushima Medical University, who carried out the study, have said they do not believe the most recent cases are related to the nuclear crisis.
They point out that thyroid cancer cases were not found among children hit by the 1986 Chernobyl nuclear accident until four to five years later.
The prefecture's thyroid screenings target 360,000 people who were aged 18 or younger when the March 2011 meltdown crisis at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear plant was triggered by a major quake and tsunami, the report said.
According to the report, last month, U.N. scientists assessing the health impact of the Fukushima nuclear crisis said the radiation dose for residents in the region was much lower than Chernobyl and that they do not expect to see any increase in cancer in the future.