Jack Hoffman, from Atkinson, had been in remission since October. His father, Andy, said doctors found a "spot of concern" in Jack's brain in April, and follow-up tests in Boston on Wednesday showed the tumour had grown.
Andy Hoffman wrote on Jack's CaringBridge page that the tumour would be treated with chemotherapy.
Jack's touchdown won an ESPY Award for best sports moment of 2013. Players mobbed him and lifted him on their shoulders in triumph after his 69-yard run. The video of the play has been replayed on national TV and viewed more than 8 million times on YouTube.