The Louisville Ironman Triathlon wasn’t going very well for Christina Mitchell. Although she was an experienced triathlete and had trained harder than ever, she lagged behind her target pace. She was in pain by the time she got off her bike to begin the marathon. During this final leg of the race, she alternated between walking and running—something she had never had to do before.

Lost in thought as she struggled, Mitchell didn’t notice the fellow competitor beside her throughout the run. He struck up a conversation at mile 18. He told her that he had testicular cancer and that training and competing in the triathlon was helping him cope with his disease and treatment.

Buoyed by his positive attitude, Mitchell was able to run the rest of the way, and they crossed the finish line together.

Mitchell didn’t know it at the time, but she had more in common with her running companion than just the same race time. She too had cancer.

Mitchell, who is 46 and lives in Tacoma, Wash., began experiencing constipation in December, two months after the Ironman. She became increasingly concerned when the constipation persisted even after increasing her fiber intake. After an X-ray and CT scan didn’t reveal anything out of the ordinary, she was referred to a digestive health specialist for a colonoscopy. Before she could get in for that appointment, she was in so much pain that she couldn’t sleep or eat.

Her primary care physician referred her to a rectal surgeon, who thought that an anal tear was the likely cause her intense pain. Surgery revealed something far more serious: a large tumor that took up most of the anal canal, which was subsequently diagnosed as stage 3b anal cancer.

“It was a shock to everyone, including myself, because I lead a very healthy lifestyle,” Mitchell says. “I’m really regimented about how I eat and see a nutritionist. I also train twice a day, six days a week. But cancer can strike healthy people at a relatively young age.”

Mitchell met with an oncologist just a few days after surgery and began a combination of radiation treatments and chemotherapy two weeks later.

“I’m hoping it’s curable, but I just take my treatments day by day,” Mitchell says. “It helps to be surrounded by people who do these triathlons and have this positive energy. You set a goal, figure out how to implement it and go for it.”

Mitchell’s cancer has put her triathlon plans on hold for now, but she plans to complete the 31-mile route of The Ride, a bicycle fundraiser for cancer research at the University of Wisconsin.

“I’d like to see more money go to research,” Mitchell says. “I think we’re on the cusp of some really good things happening in cancer research. That costs money. I just want to help raise money in any way I can, raise awareness that cancer affects people from all walks of life and add some positive energy to the event—just as my running companion in Louisville did for me.”

Donate now to Christina’s ride.