Anti β catenin antibody

Four-micrometer-thick sections were cut from FFPE tumor blocks for IHC. IHC for β-catenin was performed on a BenchMark XT automated immunostainer (Ventana Medical Systems Inc., Tucson, AZ). Sections were incubated with anti-β-catenin antibody (Cell Marque, catalog #760-4242) at a concentration of 1.73 ug/mL. Antigen retrieval was performed with Cell Conditioning Solution (CC1, Ventana Medical Systems Inc.) for 24 hours, and primary antibody incubation was for 24 hours. Antigen detection was performed using the Optiview DAB Detection kit (Ventana Medical Systems Inc.). For analysis of mismatch repair protein expression, primary monoclonal antibodies against MLH1 (clone G168-728, diluted 1:250, BD PharMingen, San Diego, CA), MSH2 (clone FE11, diluted 1:50, Oncogene Research Products, La Jolla, CA), MSH6 (clone 44, ready to use, Ventana Medical Systems Inc.), and PMS2 (clone A16-4, diluted 1:200, BD PharMingen) were used. Non-neoplastic colonic mucosa and colorectal tumors known to be deficient of MLH1, MSH2, MSH6, and PMS2 were used as external positive and negative controls, respectively. Retained expression of each protein was defined by nuclear IHC reactivity of tumor cells, whereas loss of expression for each protein was defined by the total absence of nuclear staining.