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35-Year-Old Dad Diagnosed with Stage 3 Colon Cancer After Ignoring Sharp Stomach Pain
Mark Seguin, an active snowboarder, was surprised to learn his recurring stomach issues were actually late-stage colon cancer.
Mar. 3, 2026 at 6:31am
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Mark Seguin, a 35-year-old dad and avid snowboarder, initially brushed off sharp stomach pains as something he ate, but it turned out to be stage 3 colon cancer that had spread to his lymph nodes. After undergoing surgery, high-dose chemotherapy, and a difficult recovery, Seguin committed to strength training and a healthier diet to regain his strength and reduce his risk of cancer recurrence.
Why it matters
Colon cancer is becoming more common in younger adults, now the leading cause of cancer death in people under 50. Seguin's story highlights the importance of listening to your body, getting checked out by a doctor, and not delaying follow-up care, as his early detection allowed for more effective treatment.
The details
Seguin first experienced severe, debilitating stomach pain that he attributed to something he ate. The pain would come and go over the following months. After a trip to the ER and a referral to a gastroenterologist, Seguin was shocked to learn he had late-stage colon cancer that had spread. He underwent surgery to remove part of his intestines, followed by grueling chemotherapy that left him sensitive to cold and struggling to stay hydrated.
- Seguin first experienced severe stomach pain in the morning that left him unable to get out of bed.
- About a month later, Seguin experienced the same type of stomach pain, but less severe.
- A couple more months went by before the pain returned, this time on the right side of Seguin's belly, prompting him to go to the ER.
- After the ER visit, Seguin was referred to a gastroenterologist, who performed a colonoscopy and diagnosed him with late-stage, stage 3 colon cancer.
- Seguin underwent surgery and about 5 months of high-dose chemotherapy to treat the cancer.
The players
Mark Seguin
A 35-year-old dad and active snowboarder who was diagnosed with stage 3 colon cancer.
Gastroenterologist
The doctor who performed a colonoscopy on Seguin and delivered the news of his late-stage colon cancer diagnosis.
What they’re saying
“I'm pretty sure you have cancer,”
— Gastroenterologist
What’s next
If Seguin's next scan looks good and his blood work remains clean through the rest of the year, his doctors say they will release him from oncology care, marking an important milestone in his recovery.
The takeaway
Seguin's story underscores the importance of listening to your body, getting checked out by a doctor, and not delaying follow-up care, as his early detection allowed for more effective treatment of his stage 3 colon cancer. His commitment to a healthier lifestyle, including strength training and a more fiber-rich diet, has also been crucial to his recovery and reducing his risk of cancer recurrence.
