Microsatellite instability and K-ras mutations in patients with ulcerative colitis

Area of Science:

• Gastroenterology
• Oncology
• Molecular Biology

Background:

• Patients with inflammatory bowel disease (IBD), especially ulcerative colitis (UC), face a higher risk of colorectal cancer (CRC).
• The molecular mechanisms underlying this increased cancer risk in UC patients remain unclear.
• Microsatellite instability (MSI) was hypothesized to contribute to colonic mucosal mutations and cancer predisposition in UC.

Purpose of the Study:

• To investigate the frequency of K-ras mutations in UC patients.
• To determine if MSI predisposes to K-ras mutations in UC.
• To compare molecular findings between biopsy and resection specimens from the same UC patients.

Main Methods:

• Analysis of 258 specimens from 52 UC patients, including 71 neoplastic specimens.
• K-ras mutations were detected using direct sequencing.
• MSI was evaluated using polymerase chain reaction (PCR) amplification across 8 microsatellite loci.

Main Results:

• K-ras mutations were identified in 18.2% of patients; MSI was present in at least one locus in 30.8%.
• A strong association (81.8%) of K-ras mutations involved G to A substitutions in codons 12 or 13.
• No correlation was found between MSI and K-ras mutations, even in rare high-level MSI cases. MSI was more common in regenerative mucosa, while K-ras mutations were predominantly in neoplastic mucosa.

Conclusions:

• MSI in UC regenerative mucosa does not appear to drive colonic neoplasia through a K-ras-mediated pathway.
• The low-level nature of MSI in UC may explain the lack of association with K-ras mutations.
• K-ras mutations in biopsy specimens showed a tendency to predict their presence in subsequent resection specimens.