BACKGROUND: The interesting preponderance of Chinese with colorectal carcinoma (CRC) amongst the three major ethnic groups in Malaysia prompted a study to determine DNA mismatch repair (MMR) status in our CRC and attempt correlation with patient age, gender and ethnicity as well as location, grade, histological type and stage of tumour. Histologically re-confirmed CRC, diagnosed between 1st January 2005 and 31st December 2007 at the Department of Pathology, University of Malaya Medical Centre, were immunohistochemically stained with monoclonal antibodies to MMR proteins, MLH1, MSH2, MSH6 and PMS2 on the Ventana Benchmark XT autostainer. Of the 142 CRC cases entered into the study, there were 82 males and 60 females (M:F=1.4:1). Ethnically, 81 (57.0%) were Chinese, 32 (22.5%) Malays and 29 (20.4%) Indians. The patient ages ranged between 15-87 years (mean=62.4 years) with 21 cases <50-years and 121 ≥50-years of age. 14 (9.9%) CRC showed deficient MMR (dMMR). Concurrent loss of MLH1 and PMS2 occurred in 10, MSH2 and MSH6 in 2 with isolated loss of MSH6 in 1 and PMS2 in 1. dMMR was noted less frequently amongst the Chinese (6.2%) in comparison with their combined Malay and Indian counterparts (14.8%), and was associated with right sided and poorly differentiated tumours (p<0.05). 3 of the 5 (60.0%) dMMR CRC cases amongst the Chinese and 1 of 9 cases (11.1%) amongst the combined Malay and Indian group were <50-years of age. No significant association of dMMR was noted with patient age and gender, tumour stage or mucinous type.
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