Lower prevalence of Lynch syndrome in colorectal cancer patients in a Japanese hospital-based population.

PURPOSE: The aim of this study was to investigate the prevalence of Lynch syndrome among Japanese patients with surgically resected colorectal cancer at a single institution. METHODS: Of 616 colorectal cancer patients who underwent surgical operation in our institution from January 2005 to August 2010, immunohistochemistry analyses for mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2) and microsatellite instability (MSI) testing for surgically resected, formalin-fixed paraffin-embedded colorectal cancer specimens from 138 colorectal cancer patients under 60 years of age were undertaken. Hypermethylation of the MLH1 promoter and BRAF mutation were analyzed where necessary. RESULTS: Seven patients were identified as candidates for genetic testing by mismatch repair protein loss (n = 7) or MSI-H (n = 6). Methylation of MLH1 was detected in one case. Three patients were diagnosed with Lynch syndrome, comprising 2.2 % of the total colorectal cancer patients younger than 60 years of age. CONCLUSION: The prevalence of Lynch syndrome among hospital-based diagnosed cancer patients may therefore be lower than expected in Japan compared with Western populations.