NEW YORK (Reuters Health) - People with Crohn's disease and ulcerative colitis are known to be at increased risk for colon cancer and, in a new study, researchers identify some of the factors that raise the risk.

Crohn's disease and ulcerative colitis are collectively known as inflammatory bowel diseases. With Crohn's disease the inflammation typically involves the small intestine, but it can affect any part of the gastrointestinal tract, whereas with ulcerative colitis, the disease is usually confined to the colon and rectum.

As reported in the American Journal of Gastroenterology, Dr. Edward V. Loftus of the Mayo Clinic in Rochester, Minnesota and colleagues studied 43 inflammatory bowel diseases patients with colon tumors and 102 similar patients without tumors.

The authors identified several factors that raise the risk of colon cancer in these patients. The presence of primary sclerosis cholangitis, a disease involving scarring of the bile ducts inside and outside the liver, raised the risk by nearly sevenfold.

Frequent disease flare-ups and 1 year or more of continuous symptoms increased the risk as well, the authors note.

"The findings," continued Loftus, "fit in nicely with emerging data that the degree of chronic inflammation of the colon is a risk factor for...cancer in the setting of inflammatory bowel diseases. It also confirms previous work that primary sclerosing cholangitis is an important risk factor."

Unfortunately, frequent physician visits did not lower the risk of developing cancer. Furthermore, Loftus added, "We had expected to see a protective effect of (certain) medications and colonoscopy, but did not."