Immunohistochemistry for MHL1and MSH2: a methodfor identifying mismatch repairgenein Nepalese colorectal cancer patients

Abstract

Lynch syndrome (LS)(previously known asHereditary nonpolyposis colorectal cancer(HNPCC)syndrome)iscaused bymutations inmismatch repair (MMR) genes.LSis anautosomal dominant condition accounting for 2–5% of all colorectal carcinomas.Mismatch repair genes contain mainly four genes they are MLH1, MSH2, PMS2 andMSH6. Colorectal cancers with DNA mismatch repair gene mutationscharacteristically display a high rate of replication errors in simple repetitivesequences detectable as microsatellite instability (MSI). Monoclonal antibodiesagainst hMLH1and hMSH2are commercially available, those two DNA mismatchrepair proteins accounts for mostLScancers. This study pursued to investigate thepotential utility of these antibodies in determining the expression status of theseproteins in paraffin-embedded formalin-fixed tissue and to identify key technicalprotocol components associated with successful staining.Colorectalcancersample of 43 patients of Nepal wereexaminedand immunohistochemistrywas used todetermine which tumours lacked expressionMLH1 and MSH2 gene.Out of 43patient 18.6%(8 of 43)of the sampleshowed abnormal staining patternfor hMLH1antibodyand 11.6%(5 of 43)of sample showedabnormal staining patternfor hMSH2antibodyonly 9.30% (4 of 43 ) sampleshowedabnormal staining pattern for bothantibody.The key protocol point associated withsuccessful staining was an antigenretrieval step involving heat treatmentwith Tris-EDTAheated at 121 C for 2 minutes.Tumours with mismatch repair defect were frequently foundatthe age less than 50years (p<0.05) than tumours with no mismatch repair defect. This studydemonstrates the potential utility of immunohistochemistry in detecting LSprobands and identifies key technical components for successful staining.Immunohistochemistry can bedone in local laboratories to findmismatch repairproteinsdefect on theselected cases before referring for the expensive moleculartest. Keywords:Lynch syndrome,Hereditarynonpolyposis colorectal cancer,mismatchrepair defect, colorectal cancer, paraffin-embedded formalin-fixed tissue,Monoclonal antibodies,Antigen 0