There is a definite link. I have anxiety (GAD and social anxiety) and I notice a huge correlation to my stress levels and my digestive system. I’ve been to the doctor about it and was told I’m a ‘stomach responder’, which means when I get anxious/stressed, it strongly affects me in the gut, including digestion and elimination. For example, from about June to October of 2008, I was in a horrible place, stressors from every direction, more stuff piling on every day, so bad that I just wanted to lie down and die to make it all stop. I learned then that I have IBS in reaction to stress, because I had diarrhea pretty much every day during that time. The doc recommended fiber tablets to help stimulate the inside of the intestines, and she gave me some prescription, which I now have forgotten the name.
If I were you, I wouldn’t jump straight to cancer! It could be IBS, a change in diet, exposure to different environmental flora, who knows! But don’t flip out and make yourself more anxious by worrying about cancer, that’s counter-productive. You won’t know until you talk to a doctor and there’s no sense in worrying about stuff until you know for certain what’s going on. (coming from an anxious person, I know that’s hard, but it’s one of my personal mantras)