Ben Baltz, Cancer Survivor, Carried By Marines Across Triathlon Finish Line After Prosthetic Leg Breaks (PHOTOS)

When Kim Baltz didn't see her 11-year-old son approaching the finish line at the Sea Turtle Tri kids triathlon in Pensacola Beach, Fla., she knew something was amiss.

"It was only a mile, I knew he was tired, I was like, 'Where is he, where is he, where is he,'" she told CNN's iReport.

The lower half of Ben's right leg was amputated when he was just 6 years old and diagnosed with bone cancer. He had been complaining of pain in the area after a ski trip when doctors discovered Osteosarcoma in its early stages. The now cancer-free boy uses a mechanical knee and prosthetic leg that help him walk and run, switching between two types of legs for sports and everyday movement.

But when the screw that connects the leg and knee came loose mid-race, a group of Marines -- who helped sponsor the event -- swooped in to lift him up and help him finish.

"As the group came into view, everyone started cheering louder than usual, and I saw more than a few people crying as they crossed the finish line," an observer recalled on CNN's iReport.

But the triathlon course isn't the only place Ben demonstrates his fervent perseverance. He's served as a bat boy for the Wounded Warriors Amputee Baseball Team and in September, he participated in a deep-sea fishing trip with other kids who are currently battling and have survived cancer, Gulf Coast News Today reports.

“These kids always support each other," Camp Rap-A-Hope Assistant Director Roz Dorsett told the news outlet, "and it’s just one of the reasons why I love my job.”

See more the photos from Ben's emotional finish:

SLIDESHOW: