A 31-year-old marathon runner thought she had norovirus. She was diagnosed with stage 3 colon cancer.

• Katelyn Jonozzo, 31, lived a very active lifestyle and had no symptoms of colon cancer.

• She was diagnosed in February when she suddenly felt a sharp pain and extreme bloating.

• Jonozzo needed an emergency colostomy and adapted to running with a colostomy bag.

From a young age, Katelyn Jonozzo prided herself on being very active.

Until she was 18, she practiced gymnastics 4 to 5 days a week. “I liked the discipline, I liked having a regimented schedule,” Jonozzo, 31, told Business Insider. “It instilled how important health and fitness are to your lifestyle.”

At 20, she gravitated towards marathon running. A supply chain analyst, Jonozzo regularly woke up at 4 or 5 a.m. to lift for two hours and run before going to work. In 2024, he qualified to run the Boston Marathon. He couldn’t wait to drive it in 2025.

That was before she felt a sudden, sharp pain in her stomach in February.

Jonozzo started having flu-like symptoms and vomiting. She attributed it to norovirus, which was circulating in her Cleveland suburb at the time.

“My stomach started getting really, really bloated — I looked like I was almost pregnant,” Jonozzo said. “But that was also a symptom of norovirus, so we kind of lumped it into that.”

When the pain worsened — stabbing sensations in her side and non-stop vomiting — her best friends urged her to go to the emergency room instead of waiting another day. Jonozzo complied, assuming the worst-case scenario was appendicitis.

After emergency surgery to remove part of her colon, she learned she had stage 3 colon cancer with secondary cancer in her abdomen.

Jonozzo said her training mindset helped her navigate her new reality. “I’m definitely a tunnel vision person,” she said. “I think I cried for about 30 seconds. Then I looked back at the doctor and said, ‘What’s the plan? What are we doing?’

Zero warning signs

Jonozzo said she was initially dismissed when she went to the hospital and said she might just have a stomach ache or gas. She insisted she had a high pain tolerance and wouldn’t go in unless it was serious.

Finally, he had an MRI, which revealed a three-inch tumor on his colon — one that was about to rupture.

Over the next 48 hours, she had an emergency colostomy that removed a third of her colon and installed a colostomy bag. “I was so shocked and there was so much going on that I didn’t really know what was going on,” she said.

After recovering from a catatonic state for 10 days, she learned her exact diagnosis. Her doctor estimated the tumor had been growing for about a decade, Jonozzo recalled.

“How did I run marathons?” she said. “How did I train when I had a stomach tumor?”

Training with a colostomy bag

A few weeks after the surgery, Jonozzo began his chemotherapy treatments. At first, she stayed positive by making placards with affirmations to leave around the house.

“It still never really sunk in the journey I was about to go through until I’d say probably around three or four rounds of chemotherapy,” she said.

At that time, she began to lose her hair and taste, experience skin changes and develop neuropathy, losing sensation in her hands and feet. “That’s when I realized, ‘Okay, you have cancer. This is not something we’re just going to put our heads down and get through.’

The work was a challenge. During treatment, her usual routine was excluded. “I definitely had to cut everything back,” she said. She traded long training runs and weightlifting for outdoor walks and three-mile jogs.

The biggest obstacle was the colostomy bag. “Obviously I was very aware of the bag at first,” she said. But as she began connecting with other young cancer patients through the support group The Gathering Place and the Colorectal Cancer Alliance, she began to embrace the bag.

“I’d go to the pool in my bathing suit with my bag out, or I’d lift my shirt up at the gym and tell people the bag was there, which I think just gave me confidence,” she said.

Looking for the positives helped her maintain her normal routine as long as she could. “I think it’s amazing that they’ve figured out how to get your bowel out and you can still go to the bathroom,” she said. “It’s a great tool, if you ask me.”

She runs a marathon with her cancer support group

After seven months of treatment, Jonozzo was deemed cancer-free. She finished chemotherapy in August and had a colostomy reversal in November. In mid-December, her first screening since finishing treatment, she will learn more about her upcoming screening schedule, which she already knows will include two colonoscopies a year.

She will also be officially cleared to exercise after the operation – and is keen to get back to her old routine.

“I’m a little nervous just because normally I can go out and run and do those things, but I have to take baby steps back,” she said. She plans to run three marathons in 2026, hoping to requalify for Boston through one of them.

She is especially excited about the Cleveland Marathon in May. She will lead it as team captain for her cancer fundraising group, which she said has awakened new passions in her. “I like to advocate, I like to talk to people,” she said. “I’ve always loved doing it – I just didn’t have the confidence to do it before.”

It’s just one of the ways her cancer experience has changed her, she said, along with becoming more present.

“People think I’m crazy for saying this, but I really think it was one of the best things that ever happened to me,” she said. “I wouldn’t trade this experience for anything. I really wouldn’t.”

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