Carcinogenesis in inflammatory bowel disease.

Patients with longstanding ulcerative colitis (UC) and Crohn's disease (CD) have an increased risk of colorectal cancer (CRC). CRC accounts for approximately 15% of all deaths in patients with inflammatory bowel disease (IBD). The molecular pathway leading to CRC in IBD appears to differ from the well-known adenoma-to-CRC sequence, given the fact that these cancers appear to arise from either flat dysplastic tissue or dysplasia-associated lesions or masses. The risk of CRC for patients with IBD increases by 0.5-1% yearly, 8-10 years after diagnosis. Patients with a young age at disease onset, more extensive colitis, greater inflammatory burden, concomitant primary sclerosing cholangitis, and a family history of CRC are at greatest risk. Most cancers arise in pancolitis and there is little or no increased risk associated with proctitis while left-sided colitis carries an intermediate cancer risk. The CRC risk in patients with colonic CD is similar to that of UC. Colonic dysplasia is a precursor to CRC in IBD. There is no clear evidence that surveillance colonoscopy prolongs survival in patients with extensive colitis. Newer endoscopic and molecular techniques are being assessed for their effectiveness in augmenting conventional surveillance.