Pathology and genetic markers of colorectal cancer in Lynch syndromes I and II

Approximately 6% of the total colorectal cancer burden is accounted for by hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndromes I and II. The Lynch syndrome II gene is tentatively located on chromosome 18q11-q21, as a result of significant linkage to JK (Kidd blood group). However, no specific biomarkers are available for diagnosis or screening. Thus, family history remains the key. Biomolecular studies have shown chromosomes 5, 17, and 18 to be important areas for allelic loss in colorectal cancer. A Lynch syndrome patient recently showed allelic loss on chromosome 5 polyps, while a separately arising colonic cancer showed allelic loss on chromosome 18 and not on chromosome 5. Colon cancer pathology in HNPCC has been characterized by increased mucinous adenocarcinoma, which is more poorly differentiated, with possibly increased signet cell carcinomas. Adenomas in this disease show significantly more moderate or severe dysplasia with villous features. Flat adenomas have been recently identified in HNPCC. Biochemical data has shown significantly less binding by the lectins peanut agglutinin and Dolichos biflorous agglutinin (DBA) in HNPCC. This is important in that dysplastic flat mucosa and adenomas in patients with FPC showed significantly decreased binding with DBA. In vitro cell labeling of rectal colonic mucosa by [³H]-thymidine in patients with HNPCC has shown increased uptake in the distal crypt compartment. It is clear that many gaps remain in our knowledge of genetic defects that contribute to colorectal cancer. The Lynch syndromes need to be assessed with basic pathology and the newly emerging biomolecular techniques.