I have had every cancer fear known to man. Doesn't mean I won't get cancer. I'd guess once per day or more I give it a passing thought. I am 58. This has been going on since I was 18. About 1 in 2 people get cancer... but one in two also don't EVER get it.
My thoughts on IBS. If you don't have anxiety disorder, you don't have IBS. IBS is a spastic/anxious disorder--IBS C is a motility disorder. Gluten is an allergy. To say they are the same thing shows medicine just doesn't care much. If you are the sort of person who notes and rechecks a pain... you are a great candidate.
If you have IBS, I would bet you also have considered fibromyalgia more than once, have a history of prostatitis or CPPS, or have back spasms. If you haven't, I don't think you have what I call IBS.
IBS pain moves around--it is worse if you notice a spot and keep checking to see if that spot hurts with your mind. The flexures (splenic and hepatic) are notorious pockets of painful gas. A lot of IBS pain comes from associated diverticular disease--made worse by FOODMAP or high fiber--but ultimately safer for colon cancer--which, let's face it, is the 900 kilo gorilla in the room. If you don't have gas and bloating--you don't have IBS IMHO.
About 1 in 55 people die of colon cancer. More than 70 pct of those are over 75. Facts. Can you die at 28 of colon cancer? Sadly yes. I've known a son of a friend personally. He did nothing wrong--barely smoked or drank--ate a lot of veg and fiber and had bad luck. How common is that? Maybe 1 in 10,000 or less. Could you be the one? Yes. Can you be the 9999? Yes. In your town of 10,000, someone loses... and dies of colon cancer at 28. But 9999 didn't lose. The fear neither causes winning or losing--but it does hammer your quality of life.
IBS probably has no implications for cancer. None/zero. Don't smoke. Don't drink alcohol--known carcinogens. Avoid things like dying your hair. Avoid working near benzene or in mines. Avoid being over 30 BMI. Avoid processed meats like salami, sausage, peperoni, etc. Eat more fruit and veg than anything else.
My pains are often worst at the flexures--trapped gas--squeezed by exciting. I also lock muscles into place so long they spasm. Sometimes I can feel my colon literally shaking like a bag of jam. Muscles nearby often hurt. Pain radiates to hips, collar bone--sometimes even the fronts of the shoulders--not destructive pain--just scary ever-present pain. And then it is gone. Or it progresses to a panic breakdown. I've had every possible outcome... some good, many bad. If it doesn't hurt on waking up--probably IBS.
When to be afraid enough to act:
A. Blood--especially streaky blood in poo demands an explanation.
B. Rapid weight loss with anemia --requires explanation.
C. Symptoms without anxiety or history of anxiety/panic or similar.
D. If medical tests don't frighten you and do give you comfort.
Otherwise, treat it as a physical manifestation of mental health--and anyone who doesn't think mental health has profound physical manifestions--simply doesn't understand much about mental health.
My opinions--not advice. Be well.