(UPDATE) Kyodo News just reported it was a girl, age 16 to 18.
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The first confirmed case of thyroid cancer in a child in Fukushima Prefecture was reported in September this year, after the 2nd screening test which was administered as a precaution.
Possibly the second one may have been found, according to Kahoku Shinpo. What's different in this case is that the child was immediately categorized as "C" in the 1st round of screening. Category C is "in need of immediate second testing", according to the Fukushima prefectural guideline.
From Kahoku Shinpo (11/17/2012):
甲状腺がんの疑い 福島県直ちに2次検査、初めて1人判定
One case of suspected thyroid cancer, Fukushima Prefecture to conduct further test immediately
東京電力福島第1原発事故による放射線の影響を調べるため、福島県が18歳以下の約36万人を対象に行っている甲状腺検査の1次検査で、がんの疑いがあり「直ちに2次検査が必要」と初めて判定された子どもが1人いることが17日、関係者への取材で分かった。
Fukushima Prefecture has been conducting the thyroid testing of about 360,000 children under the age of 18 to understand the effect of radiation due to the Fukushima I Nuclear Power Plant accident. It was revealed on November 17 by the source that they found one child during the initial screening who may have cancer and is in need of immediate second testing.
18日に開かれる「県民健康管理調査」検討委員会で報告される。
The details will be reported in the meeting of "Fukushima Prefecture residents health management survey" committee on Novmeber 18.
調査を進めている福島県立医大は「チェルノブイリ原発事故でも甲状腺がんの発見に最短で4年かかった」として、放射線との因果関係は低いとみているが、血液や細胞を調べ、がんかどうか判断する。
Fukushima Medical University, who has been conducting the test, says "It took 4 years to find a thyroid cancer after the Chernobyl nuclear accident", and the possibility of relationship between the radiation [from the Fukushima accident] and the potential thyroid cancer is low. However, blood and tissue samples will be taken to determine whether it is a cancer or not.
1次検査による判定は、しこりの大きさなどを基に、軽い方から「A」「B」「C」があり、今回の1人は「C判定」。
There are three categories, A, B and C, in the initial screening depending on the size of nodules/cysts. The child in question was judged to be in the "C" category.
9月の検討委では、緊急性は低いが念のため2次検査が必要という「B判定」だった1人が、甲状腺がんと判明したと報告された。だが、がんの状態から「震災以前に発症していた疑いがある」として、原発事故の放射線との因果関係を否定している。
In the committee meeting in September, it was reported that one child under "B" category (no immediate action necessary but conduct the 2nd test just in case) was found with thyroid cancer. However, judging from the state of the cancer, the committee thinks the cancer had already been developing before the March 11, 2011 disaster and denies the causal relationship between the radiation from the nuclear accident and the cancer.
県立医大は「県内全ての子どもの検査という前例のない調査なので、早期発見の子は少なからず出る。放射線との関係を丁寧に調べていく」としている。
Fukushima Medical University says, "This is an unprecedented study of all children in Fukushima Prefecture. So it is expected that a fair number of children are found with thyroid cancer. We will carefully study the relationship between the radiation [and the thyroid cancer]."
According to the Fukushima prefectural government (as of September 2012), the testing schedule for the cities in Fukushima is as follows (English labels are mine):