Patient and tumor characteristics of colon cancers with microsatellite instability: A population-based study

Molecular screening for microsatellite instability (MSI) in colon cancers h as been proposed to identify individuals with hereditary nonpolyposis color ectal cancer. To date, most reports of MSI in colorectal cancer have been b ased on studies of clinical case series or high-risk families. We examined the proportion of incident colon cancers in the general population that exh ibit MSI by patient and tumor characteristics. We interviewed 201 colon can cer cases ascertained by the New Mexico Tumor Registry in the metropolitan Albuquerque area for demographic information, lifestyle factors, medical hi story, and family cancer history. Paired normal and tumor tissue specimens were obtained for each case. Three microsatellite markers were used; instab ility was defined as observed alteration at two or more loci, Overall, 37 o f 201 (18%) colon cancers exhibited instability. MSI was more common among cases >70 years (26%) and most common among cases >80 years (38%). MSI was significantly associated with tumors in the proximal colon and with later s tage and poor differentiation among cases >70 years, MSI was not associated with a history of polyps, Family history of colorectal cancer was associat ed with MSI only among cases <50 years. When all factors were analyzed join tly in a regression model, proximal subsite and poor differentiation remain ed significantly associated with MSI. One patient, whose tumor exhibited MS I, fulfilled the Amsterdam Criteria for hereditary nonpolyposis colorectal cancer. Our study provides a population-based estimate of MSI in colon tumo rs and a representative estimate of the proportion of colorectal cancer pat ients in the general population who consent to be interviewed for family ca ncer history and to have biological samples analyzed.