Colorectal cancer in inflammatory bowel disease: the risk, pathogenesis, prevention and diagnosis

Abstract

Patients with inflammatory bowel disease (IBD) are at increased risk for developing colorectal cancer (CRC), although the overall incidence of IBD-associated CRC has been diminishing in recent decades in western countries. As demonstrated in previous studies, the risk of CRC in IBD increases with longer duration, extent of colitis, a familial history of CRC, coexistent primary sclerosing cholangitis, and the degree of inflammation. The pathogenesis of CRC in IBD is poorly understood. Similar to sporadic CRC, IBD-associated CRC is a consequence of sequential episodes of genomic alteration. Multiple inter-related pathways, including immune response by mucosal inflammatory mediators, oxidative stress, and intestinal microbiota, are also involved the pathogenesis of IBD-associated CRC. Continuing colonic inflammation appears to be a factor in the development of CRC; therefore, anti-inflammatory agents such as 5-aminosalicylate compounds and immune modulators have been considered as potential chemopreventive agents. Colonoscopic surveillance is widely accepted as being effective in reducing the risk of IBD-associated CRC, although no clear evidence has confirmed that surveillance colonoscopy prolongs survival in patients with extensive colitis. The traditional recommendation has been quadrantic random biopsies throughout the entire colon; however, several guidelines now have endorsed chromoendoscopy with a target biopsy because of increasing diagnostic yields and reduced workloads for endoscopists and pathologists. New technologies such as narrow band imaging, confocal endomicroscopy, and autofluorescence imaging have not yet been confirmed as surveillance strategies in IBD.

Keywords: Chemoprevention; Colorectal cancer; Inflammatory bowel disease; Pathogenesis; Surveillance.

Figure 1

Molecular pathogenesis of sporadic colon cancer and colon cancer associated with inflammatory bowel disease. Many of the genetic alterations associated with development of sporadic colon cancer also play a role in colitis associated colon cancer. However, the frequency and sequence of these events differ between the cancers. Modified from Ref [21]. APC: Adenomatous polyposis coli; MSI: Microsatellite instability; KAS: Kirsten Rat Sarcoma Viral Oncogene Homolog; COX-2: Cyclooxygenase-2; DCC: Deleted in colorectal carcinoma; DPC4: Deleted in pancreatic carcinoma 4; CIN: Chromosomal instability.