Thanks for your reply Ides. I admit it is a very weird thing, but I've been told by more than one doctor that I have a lot of little weird eccentricities with my body. My mom was always told the same thing :)
That makes me feel better that perhaps the laxative use is the trigger for the cancer, and not the melanosis coli in and of itself. I wish medicine did less flawed research.
As far as getting an answer from a doctor, I'm sure it won't happen. I've asked 3 doctors and they all insist that I must have used senna laxatives at some point; there is no other explanation. My response has always been, "If I was a routine user of laxatives, wouldn't you at least think I'd be skinny? And not constipated?"