Microsatellite instability and hMLH1 and hMSH2 gene expression in Taiwanese hereditary nonpolyposis colorectal cancer

The mutation rate of hMSH2 and hMLH1 (20%) in Taiwanese hereditary nonpolyposis colorectal cancer (HNPCC) is lower than that reported in other countries. This study aimed to examine the microsatellite instability (MSI) status and gene expression pattern of Taiwanese HNPCC in an effort to establish correlation between these data and results of prior genetic screening.

The "Bethesda markers" were used for the MSI analysis. Tumor and neighboring tissues were obtained from 10-mm sections of neutral formalin-fixed, paraffin-embedded, hematoxylin and eosin-stained specimens with a PixCell laser-capture microdissector. Four-mm sections were used for the immunohistochemical analysis by avidin-biotin complex method and final coloring with diaminobenzidine. A pathologist performed scoring of the pathological specimens twice, using a double-blinded methodology. Thirteen tissue blocks from 8 HNPCC families (Amsterdam's criteria) were included in this study.

Although the majority of the HNPCC tissues displayed a MSI-high phenotype (10/13, 76.9%), lack of expression of MSH2 and MLH1 was infrequent. Furthermore, only 1 germ-line mutation was detected in the peripheral blood leukocytes of the patients whose tumors had lost protein expression of MSH2 or MLH1.

Our results indicate that the pathogenesis of Taiwanese HNPCC is different from that in other countries. Rather than immunohistochemical analysis, MSI status, and genetic screening, clinical history remains a reliable method for diagnosis of HNPCC in Taiwanese the population.