Man Diagnosed With Colon Cancer at 35 Only Had One Symptom

This as-told-to essay is based on a conversation with Mark Seguin, who was surprise-diagnosed with colon cancer five years ago at age 35. It’s been edited for length and clarity.

I’ll never know for sure why I got colon cancer at age 35.

Sure, I can look back now and point to things that weren’t perfect. Work stress, ultra-processed foods, having two young kids, I wasn’t taking care of my body in exactly the way that I used to — especially after weathering several snowboarding injuries, I kind of slowed down on my fitness. But I don’t feel like it’s healthy to “would have, could have, should have” about cancer or blame yourself. Especially because some people in peak physical fitness with the cleanest diets get this disease.

There weren’t really any obvious signs that I was sick. Just one day, I woke up and it hit me. A searing pain in the middle of my stomach as soon as I opened my eyes. I literally could not get out of bed. The pain was so bad, I couldn’t get my body upright. It felt like someone was ringing out a rag inside of me.

I’d later learn this was because — unbeknownst to anyone — food was getting stuck behind the tumor in my colon. Unable to move through my system properly, waste was building up and wreaking havoc.

I just assumed I ate something bad the day before. I wondered what it could have been.

By the afternoon that day, I was feeling better, and I got up and carried on. But about a month later, it happened again. This time, it was the same type of stomach pain, but not as severe. Again, I was like, “Man, what am I eating that keeps doing this to me?”

A couple more months went by. Then again, the pain returned, this time on the right side of my belly. Alarm bells went off. I immediately thought of all the stories I’ve heard about people ignoring stomach pains, and then their appendix ruptures and bursts. That was my wake-up call to get myself to the ER and get checked out. Still, cancer was not on my radar. I never saw any blood in the toilet, so I didn’t think I had to worry about colon cancer.

After searing stomach pain, and a trip to the ER, a GI doctor finally found my cancer

Thankfully, I didn’t have appendicitis, but my ER doctor referred me to a gastroenterologist for some follow-up tests. The GI doctor said I was young, healthy, and there was probably nothing to worry about, but suggested we do a colonoscopy, just to be safe.

I’ll never forget the look on his face when he walked in to deliver my results. He looked like he’d just seen a ghost. “I’m pretty sure you have cancer,” he said. It was serious too: late, stage 3 colon cancer that had spread to my lymph nodes. He said I won the bad luck lottery.

I reacted like I always do when I get hurt snowboarding, break a bone, or throw my back out: What’s the next step? I have to know what to do next.

Surgery, draining high-dose chemotherapy treatments, and lots of days in bed. That’s what came next. The chemo made me super sensitive to cold. Breathing cold air or drinking cold water felt like pulling apart velcro in my throat. I couldn’t drink anything cold or enjoy popsicles to stay hydrated, but warm liquids made me nauseous. I became hyperattuned to even the smell of water, and it repulsed me. I had to get hooked up to intravenous hydration roughly half a dozen times while going through chemo because I just couldn’t eat or drink much of anything.

After colon cancer, I committed to more strength training

By the time I rang the bell and finished chemotherapy, about five months after my diagnosis, I felt so frail and small. I’d lost 30 pounds. I hated feeling that way. I wanted to be able to pick up my kids when I needed to. My youngest was only 5 years old when I was diagnosed. I can’t let my boys outrun me just yet! So at the end of my chemotherapy course, I started a strength training program. It was the same one I’d used in high school that helped me get stronger, a program from a baseball fitness coach who helps train pros, including the New York Yankees, Eric Cressey.

At first, I was worried: was training safe for a cancer patient? Could it derail my recovery? And would I even have the energy? Initially, after chemo, even short hikes were draining, but I pushed forward, including squats, presses, and broad jumps into my routine.

It turns out, there’s a pretty wide and growing body of evidence suggesting that working out is great for cancer rehab — and especially for colon cancer. After about six months, I was thrilled to be setting all-time bests for my lifts and presses. It was such a proud moment.

There was a super compelling new study that I came across in 2025, which shows that exercise can be as effective at preventing colon cancer relapse as drugs. It was a wild finding that shook oncologists and excited doctors nationwide when it was revealed last year at the nation’s largest cancer conference. I’m just glad I have more reasons to keep doing what I’m doing. Right now, my routine is a basic two days a week of strength training, plus some cardio like hikes with a weighted vest or an incline treadmill jog when I can fit it in.

Part of what motivates me to work out is the idea of staying healthy and cancer-free, and — I must admit — part of it is just my dad pride. My youngest wants to race me all the time. He’s 10 now, I can’t let him beat me yet, okay?

I eat healthier now, but I’m a realist

I have also changed up my diet, incorporating more fiber-rich foods into my routine. I was raised in the “fast-food era,” but now I try to avoid the ultra-processed and cured meats that are so clearly linked to more colon cancer, like sausages, hot dogs, and bacon. (I rarely have bacon now, which sucks.)

I try to incorporate more veggies and beans into my diet, things that we know are good for colon health. In true Mediterranean Diet fashion, I try to make sure dinners include something green — if it’s chicken, I might add some broccoli, if it’s spaghetti, let’s dish up a side of green beans. I’m not perfect about it, but I think any little effort helps. When I make tacos now, I mix the ground beef with some mashed black beans. That way, it’s a little bit less meat, but also you’re getting fiber from the beans. I haven’t overhauled my diet completely, but I’ve been finding the little evidence-backed opportunities, which I think is honestly a more realistic strategy.

It’s been five years since my cancer diagnosis now, and I’m almost in the clear. My doctors say if my next scan looks good, and my blood work remains clean through the rest of the year, they’re going to release me completely. It’s kind of a scary prospect to go out into the open world without your oncology team looking out for cancer. I’ve found peace knowing I am doing a lot of the things we know decrease the odds of recurrence: exercising more, eating better, and decreasing stress. I also take a baby aspirin, which recent studies have suggested may reduce the risk of recurrence of certain types of colon cancer.

3 rules to live by for finding colon cancer

I try to always remember a few things that can help identify colon cancer early, and share them with my friends when I can.

• First of all, if something feels off, go get it checked out.
• Second: make that follow-up appointment.

My doctor said the one thing I did that so many folks miss is actually going in for that next appointment, after leaving the ER. Don’t delay the care that might save your life.

• Finally, if you’re 45, get a colonoscopy.

I know, we snowboarders like to tough things out sometimes. Don’t do that with your colon. I’m not going to miss an opportunity to say, “Hey, you’re 45, right? Did you get that colonoscopy booked?”

I try to keep it casual and not be the colon cancer weirdo out on the slopes, but I do want to advocate for more awareness of young colon cancer. Colon cancer is now the leading cause of cancer death in people under 50 — and the only cancer that’s becoming more deadly in my age group, not less. If I can help one more person get checked and find cancer earlier, that’s success.