Hyperplastic polyps in hereditary nonpolyposis colorectal cancer

OBJECTIVES: Hereditary nonpolyposis colorectal cancer (HNPCC) is a genetic syndrome caused by germline mutations in DNA mismatch repair (MMR) genes, in particular hMLH1, hMSH2, and hMSH6. Dysfunction of MMR genes leads to loss of MMR protein expression and to microsatellite instability (MSI). MSI is also detected in 10-20% of sporadic colorectal cancers. Hyperplastic polyps (HP) may serve as precursor for these MSI+ sporadic colorectal cancers. The aim of this study was to examine whether hyperplastic polyps are also possible premalignant lesions in HNPCC. METHODS: All HPs resected from (suspected) mismatch repair gene mutation carriers were retrieved from a screening program database. Clinical information on patient age at colonoscopy and location of the HP was collected. MLH1, MSH2, and MLH6 protein expression was evaluated using immunohistochemistry. RESULTS: A total of 90 HPs were resected from 21 men and 19 women. The mean patient age at resection was 45.7 yr (44.7 yr in men and 46.6 yr in women). In all patients, 19 (21%) HPs were resected from the proximal colon, 23 (26%) from the distal colon, and 48 (53%) from the rectum. None of the HPs demonstrated loss of MMR protein expression. CONCLUSIONS: Mismatch repair dysfunction in HPs of HNPCC patients is apparently very rare. It seems unlikely that HPs in HNPCC patients are precursors for (MSI+) cancers in these patients.