Crohn's and Colon Cancer: The Risk

I have Crohn's disease and my father died of cancer in his intestinal tract. Does this mean that I have two risk factors for intestinal or colon cancer, or just one? The thought led me do some research.

Most authorities agree that after having Crohn's disease (or ulcerative colitis) for a long time (translated in most articles as over 8 years of severe symptoms), you have an increased risk of getting colon cancer, or even cancer of the small intestine. One physician writes "Colorectal cancer is a significant clinical problem for patients with long-standing.... Crohn's disease" (Itzkowitz, 1997, abstract). He adds that some more recently noted factors, such as primary sclerosing cholangitis (an inflammation of the liver's bile ducts that is often associated with inflammatory bowel disease, or IBD), folate (or folic acid) deficiency, and a genetic predisposition to colon cancer (a family history), also affect a Crohn's patient's likelihood of getting colon cancer. Other sources, such as medicinenet.com and intellihealth simply say that for Crohn's patients there is an increased risk of cancer of the colon or intestines.

But what is the risk? The physicians at the Mayo Clinic (see citation below) say that "more than 90% of people with inflammatory bowel disease never develop cancer (p.7; my emphasis). The Crohn's and Colitis Foundation of America (CCFA) in their brochure "Understanding Colorectal Cancer," reiterate that statistic, and go on to explain that two risk factors can increase your risk of cancer with an IBD. They are how long you've had it (8 to 10 years, according to the brochure) and "the extent of the colon that is affected by colitis" (p. 3). They note that there is some variation in statistics between different studies, but that after 10 years, the risk of getting colon cancer increases at a rate of 0.5% per year for both Crohn's disease and ulcerative colitis.