I really think after having this for ten years you would at the least be in pretty bad shape if not dead. BUT, you should have a scope. Go back to your doc and insist on one and if he won't give you one, go to a different doc. Print out the stories of us on here (or the youngins anyway) and show it to him. It could be a fatty tumor, hernia, who knows but the answer from him of "I don't know what it is" is not a good response. He needs to find out what it is to at least give you peace of mind. Seriously though, I doubt it's colon cancer but you never know for sure.
Be tough and fight for what you need...a colonoscopy!