Dr. Thomas Haveron said Chattanooga's Tristin Greer has had to grow up too fast.

At 15, with the rare cancer neuroblastoma, the Chattanooga School for the Arts and Sciences sophomore, is advanced for his age, the Harrison, N.J., chiropractor said.

"Tristin," said Dr. Haveron, of meeting the teenager for the first time earlier this summer at Yankee Stadium, "was mature. He was an adult sooner than he should have been."

Through the chiropractor's foundation, Medicine Via Philanthropy (MVP), Haveron said he wants to encourage kids like Tristin, who have had to face adult issues as children.

With the help of the foundation, Tristin has attended additional Yankees games, the Brickyard 400 at the Indianapolis Motor Speedway, a baseball game in Detroit. He even threw out the first pitch at a Cleveland Indians baseball game.

Not bad for a guy whose favorite sports are soccer and baseball.

"There were so many free tickets [available]," Tristin said of being a patient at Memorial Sloan-Kettering Cancer Center In New York City, "that [Jason Greer, his dad] freaked out. They were such ridiculously good seats that he made me go."

Dr. Haveron originally set up his MVP foundation to help educate bright students who otherwise couldn't afford medical school. Meeting Tristin this summer, he said, caused him to make the purpose of his foundation twofold.

"It's his personality," he said. "Ninety-nine percent of health care is mental. If you think you've lost the battle, you're done. He does not have that outlook on life."

INCREDIBLE ATTITUDE

Although Tristin began his battle with cancer in March 2010, his positive attitude has been a lifelong trait, according to Jason Greer.

"He's always had a really good attitude about everything," he said. "He's a loving kid. This would make a lot of kids really down, but he's maintained an incredibly positive attitude."

Neuroblastoma is diagnosed in only 650 children, mostly very young children, in the United States each year, said Greer. The diagnosis in teenagers is only 5 percent of the larger number, he said. Memorial Sloan-Kettering, he said, has a team dedicated to the cancer and is the leading center for the disease's treatment.

After Tristin had surgery in August 2010 to remove a tumor that "encompassed his whole abdomen," according to his father, he's had numerous rounds of chemotherapy. Those included several cutting-edge regimens, including one he's just begun and is only the second one to get.

Although his son can have blood counts taken and be given some chemotherapy at Children's Hospital at Erlanger hospital, Greer said most of the treatments have required trips to New York once or twice a month.

"It's a lot of traveling," he said. "You have to miss school, be away from friends. It would be easy to get depressed about things."

Tristin said he can't put his finger on why he's remained so positive but thinks it might just be in his personality.

"I never think about the negative," he said.

The elder Greer said his son's stage IV neuroblastoma has a 30 percent survival rate but also has a high relapse rate.

"[Tristin] has several spots on his bones and his liver," he said, "so he has a ways to go. It doesn't happen overnight. But you keep going, trying different things. Even if you have NED (no evidence of disease), he'll have to have scans every month. It's a lifelong challenge."

LIGHTENING THE LOAD

Dr. Haveron said his desire to help Tristin and others like him was fueled by the fact he lost his mother and "three quarters of my family" to cancer.

"Everybody's either been affected or knows somebody who's been affected by cancer," he said.

At the Yankees game when he met Tristin, noted his maturity and learned of his situation, Dr. Haveron said he asked the teenager if he'd like him to get him a game ball.

"Sir," he remembered the bald Chattanooga student joked back to him, "when you look like me [the players] throw you things. Would you like me to get you one?"

Dr. Haveron was hooked and since then has thrown himself into offering to lighten the load where patients, health care, suffering and sports intersect. Among the other children his foundation gave a lift to recently was Max Ransom, brother of Emily Ransom, a Chattanooga youngster who died of neuroblastoma in 2006.

"No way do I want to compare myself to [the patients]," he said, "but I'd jump through hoops of fire with these kids. It all has to do with kids, the kids affected by the horrors of cancer. With these things, there's maybe no week."