METHODS: Fifty selected CRC cases of deficient mismatch repair (dMMR) and proficient mismatch repair (pMMR) which were identified immunohistochemically in the previous study were subjected to MSI analysis. MSI Analysis System 1.2 (Promega) was utilized.

RESULTS: The results of MSI analysis method showed MSI-High: 26% (13/50), MSI-Low: 6% (3/50), and Microsatellite Stable: 68% (34/50). The concordance was perfect (0.896, Kappa value) between MSI analysis and IHC methods for the assessment of MMR/MSI status in CRC patients. The discordance was only 4% (2/50). MSI analysis identified all dMMR cases determined by IHC except one case. The obtained frequency of dMMR and pMMR patients was 11.4% (14/123) and 88.6% (109/123) by IHC method, respectively.

MATERIALS AND METHODS: A total of 17 patients were selected fulfilling one of the Bethesda criteria: colorectal cancer diagnosed in a patient aged less than 50 years old, having synchronous and metachronous colorectal cancer or with a strong family history. Immunohistochemical staining was performed on paraffin embedded tumour tissue samples using four antibodies: MLH1, MSH2, MSH6 and PMS2.

RESULTS: Twelve out of 17 patients (70.6%) were noted to have a family history. A total of 41% (n=7) of the patients had abnormal immunohistochemical staining with one or more of the four antibodies. Loss of expression were noted in 13 tumour tissues with a negative staining score <4. Of 13 tumour tissues, four showed loss expression of MLH1. For PMS2, loss of expression were noted in five cases. Both MSH2 and MSH6 showed loss of expression in two tumour tissues respectively.