(CNN) -- New England Patriots players sang "Happy Birthday" to a 6-year-old boy with an inoperable brain tumor Saturday.
Daniel Nickerson's visit on the field of Gillette Stadium, where the NFL team was practicing, would be a dream come true for many. However, Daniel's biggest birthday wish was much simpler: mail.
"He just loves getting mail, he's always running to the mailbox," his aunt, Gail Chamberlin, told CNN.
A social media campaign by family and friends brought lots of birthday cards addressed to Daniel to the Foxborough, Massachusetts, post office this past week. It also resulted in the Patriots' invitation to their training camp.
Team owner Robert Kraft presented a jersey to Daniel on Friday, his actual birthday. "Danny" and the number 6 are on the back of the jersey. Kraft invited the boy back on Saturday to a practice, where he huddled alongside Tom Brady and the rest of the team. The birthday song was "the highlight of the day," his aunt said.
Daniel, who was diagnosed with Diffuse Intrinsic Pontine Glioma eight months ago, has a tumor that is inoperable because it "grows like fingers into the brain," Chamberlin said. "It was very devastating to the family to find out there really weren't any options."
His latest exam showed that the chemotherapy, which the boy will have every two weeks for the rest of his life, has stabilized the tumor's growth, she said. "It didn't grow and it didn't shrink, so we were happy about that," Chamberlin said.
When his family asked Daniel what he wanted for his sixth birthday, he told them he just wanted mail. "He just wanted news, he loves, loves getting mail, seeing things with his name on it," Chamberlin said.
The large amount of mail -- which his aunt said was at least 100,000 letters and 8,000 boxes from all over the world -- has "been a blessing" and gives Daniel something to look forward to each day, she said.
While the family is anxious about what they'll learn about the tumor at Daniel's next doctor's visit Wednesday, Chamberlin said, "He's running around like an average 6-year-old would do, playing."
"We are all praying it's stable still," she said. "No one really has lived past a year, we know we are on month eight. But we don't really talk about it and we hope there is going to be a cure."
As for Daniel, "He knows he has a 'boo boo' and that's really it," she said.