Hi there ~
I understand your concerns and I am sure that you have been suffering from IBS for a long time. It has been proven that diarrhea
that are related to this disorder are also related to the stress
levels that one experiences. Nevertheless, ruling out GI disorders would be a good idea. I think that getting a lower GI colonoscopy
would relieve your anxiety
regarding your having cancer. I think that your should also have a psychiatric consultation as it would be very helpful to see what other things (other than GI) can be changed in your life to benefit your overall health. I hope this helps.
Take care and have a lovely day!