After Colon Cancer at 35, Runner Dad Takes on the Boston Marathon With His Doctor

Crossing the finish line at the Cleveland Marathon in 2023 should have marked the beginning of John B. Johnson’s next goal. The 35-year-old runner had finally qualified for the Boston Marathon after years of training. But just two weeks later, a colonoscopy revealed a mass that was most likely cancer, replacing months of race preparation with a fight he never expected to face.

A Symptom He Nearly Dismissed

Johnson had noticed blood in his stool while preparing for the Cleveland Marathon. His primary care physician urged him to schedule a colonoscopy, but, like many active people, he assumed the symptom was probably caused by hemorrhoids and waited until after the race. The procedure instead uncovered a mass that doctors believed was cancer, delivering life-changing news just as he and his wife were preparing to welcome their second child.

The Road Back Began In A Hospital

After the diagnosis, Johnson was referred to Cleveland Clinic colorectal surgeon Dr. David Rosen. Tests confirmed stage 2 colorectal cancer that had not spread beyond the rectum. Johnson underwent five weeks of radiation followed by four months of chemotherapy, and in January 2024, scans showed no remaining signs of cancer.

A Doctor Became A Training Partner

What began as a doctor-patient relationship gradually developed into a friendship. As Johnson recovered, he and Rosen decided to train together for the Boston Marathon in 2025 while raising money for DetecTogether, a nonprofit focused on early cancer detection. For Rosen, the race became an opportunity to support a former patient outside the hospital. For Johnson, it was a chance to finish the journey cancer had interrupted.

His Story Reflects A Growing Concern

Johnson’s diagnosis at 35 mirrors a troubling trend that doctors are seeing more often. Colorectal cancer has historically been associated with older adults, but physicians are reporting increasing numbers of younger patients. Dr. Rosen told WOIO that the rise in early-onset colorectal cancer is especially concerning because researchers still do not fully understand why it is happening.

Why Early Detection Can Change Everything

The Centers for Disease Control and Prevention estimates that 155,662 new colorectal cancer cases were reported in the United States in 2023, while 54,468 people died from the disease in 2024. Yet outcomes improve dramatically when the cancer is caught before it spreads. According to CDC data, the five-year relative survival rate is 89.3% for localized colorectal cancer, compared with 16.4% once it has spread to distant parts of the body.

Breaking The Silence Around Symptoms

Johnson has since made sharing his story part of his recovery. In an account for PEOPLE, he said many people in their 30s rarely talk about colon cancer, colonoscopies, or symptoms such as blood in the stool. He hopes that openness encourages others to seek medical care sooner, and says friends have since told him they decided to get checked after recognizing similar warning signs.

Boston Became More Than A Finish Line

When Johnson and Rosen lined up together at the 2025 Boston Marathon, they were no longer simply runner and surgeon. They had spent months training through Ohio winters, raising money for colorectal cancer awareness, and proving that recovery can extend well beyond the final treatment session. Completing the race marked a milestone neither thought possible when they first met in a clinic.

One Story, Many Others

Johnson’s experience cannot explain every colorectal cancer diagnosis, nor does it represent every patient’s outcome. But doctors hope stories like his encourage people to recognize symptoms earlier instead of assuming they are too young, too fit, or too healthy to be at risk. As awareness of early-onset colorectal cancer grows, many physicians see those conversations as an important step toward earlier diagnoses and better outcomes.

A Victory That Continues Beyond The Race

Crossing the Boston Marathon finish line in 2025 closed a chapter that had begun with an unexpected diagnosis two years earlier. Johnson continues to speak publicly about his experience, hoping it encourages others to listen to their bodies and seek medical care when something feels wrong. The marathon may have fulfilled a longtime personal goal, but the message he carries beyond the finish line has become just as meaningful.