BRAF V600E Immunohistochemical Stain in Colorectal Carcinomas
Kajsa Affolter, Sam Page, Sheryl Tripp, Mary Bronner, Wade Samowitz. University of Utah Health Sciences Center, Salt Lake City, UT; ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT
Background: The serine/threonine-protein kinase B-raf (BRAF) is an oncogene mutated in various neoplasms, including five to ten percent of colorectal carcinomas. The T1799A point mutation, responsible for a large majority of these alterations, results in a valine to glutamate amino acid substitution at position 600 (V600E) and causes the constitutive activation of a protein kinase cascade. BRAF V600E in MLH1 deficient tumors implicates somatic tumor-only methylation of the MLH1 promoter region instead of a germline mutation. BRAF V600E also predicts poor prognosis in microsatellite stable colorectal cancers and may also be a marker of resistance to anti-EGFR therapy in metastatic disease. Currently, only molecular methods are available for assessing BRAF mutational status. An immunohistochemical approach is evaluated here.
Design: Serial colon cancers from 2008 to 2012 tested by pyrosequencing for BRAF V600E mutation were selected for study. A total of 14 formalin-fixed paraffin-embedded tumors with the BRAF V600E mutation and 17 without it or other BRAF mutations were analyzed by immunohistochemistry using a commercially available mouse monoclonal antibody to BRAF V600E.
Results: All 14 colorectal carcinomas with the BRAF V600E mutation demonstrated cytoplasmic positivity in tumor cells with the anti-BRAF antibody. In a minority of cases the staining intensity for the mutated tumor samples was weak or heterogeneous; however, the majority of cases showed diffuse cytoplasmic positivity. None of the 17 BRAF wild type colorectal cancers showed immunoreactivity to the anti-BRAF V600 E antibody.
Conclusions: Detection of the BRAF V600E mutation in colorectal cancer by immunohistochemistry is a viable alternative to molecular methods. This option may allow laboratories able to do immunohistochemistry but not high complexity molecular analysis to perform BRAF V600E mutational testing. It may also prove to be a more cost effective approach. Furthermore, it provides an option for detecting mutational status in cases not amenable to molecular testing, such as samples with very few tumor cells or samples with numerous contaminating non-neoplastic cells.
Monday, March 4, 2013 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 87, Monday Morning