Because Katy Miles is a pretty active 17-year-old — she hits the gym four or five times a week — you'd never guess the UK-based teen's body literally runs on just one kidney: Cancer struck her left kidney when she was 4 years old. But after 12 years in remission, Katy ran her first half marathon last weekend to raise money for the disease that nearly took her life.When Katy was a young child, her doctors insisted she had constipation, nothing more. "I just had a feeling that something else was wrong and kept going back until she was sent for a scan," says Louise Miles, Katy's mom and regional fundraising manager for the UK charity Teenage Cancer Trust. "I can remember looking on the screen, seeing a huge tumor, and knowing this was serious."Katy spent 10 months in and out of hospitals battling kidney cancer. Although the disease also spread to her lungs, she was given a 60 percent chance of survival, despite a potentially life-threatening infection in the intravenous line delivering her chemotherapy. While Katy's memory of having cancer is vague, she does recall her mom rewarding her with princess costumes if she agreed to take her foul-tasting medicines every day. To live her best life while in treatment, Katy often dressed as Cinderella, her favorite princess, during chemotherapy sessions.When Katy turned 17, the minimum age to run the Great North Run, a large half-marathon that's held near the oncologist she continues to visit for annual checkups, she decided to don a Cinderella dress again for a wonderful cause; she planned to race in the dress and use the event to raise money for the Teenage Cancer Trust. The teen raised about $1,629 and ran alongside her dad, who'd run the race before. A family affair! "After running I was completely shattered," Katy wrote in a blog post published on the charity's website after the race, which she finished in 2 hours, 54 minutes, and 32 seconds. "But I really enjoyed it...I nearly lost my shoe, just like Cinderella, at mile 3 when my lace came undone, but managed to keep it on." Still, Katy's biggest racing hurdle had nothing to do with her sneakers or even her costume, which had a hooped skirt that kept the fabric away from her legs. Around mile 6, the part of her back where she'd received radiotherapy back in the day began to ache. (Radiation treatment can slow the growth of children's muscles, according to information from The American Cancer Society.) "I had to grit my teeth the next 7 miles, as I was determined to finish," she said.And she did — with her Cinderella makeup miraculously intact — and she received countless "Go Cinderella!"s along the way.Next year, Katy hopes to run the race again as Cinderella or another Disney character — perhaps this time, a queen would be more fitting.