Grogan, Thomas M.

3576 Background: BRAF encodes a serine-threonine kinase that is a downstream effector of activated RAS. A point mutation (V600E) in BRAF occurs in a subset of colorectal cancers (CRCs) and is associated with adverse outcome and may predict non response to anti-EGFR antibodies. Detection of a BRAFV600E mutation in a CRC with microsatellite instability indicates a sporadic origin and excludes Lynch Syndrome. While BRAFV600E mutation status is determined using a DNA-based assay, antibodies against the BRAFV600E protein have recently been developed. We examined mutant BRAFV600E protein expression and its concordance with mutation status. Methods: Primary stage III colon carcinomas (50 BRAFV600E mutation carriers and 25 wild-type cases) were studied from a completed phase III adjuvant trial comparing FOLFOX +/- cetuximab (NCCTG N0147). In archival resection specimens, immunohistochemistry (IHC) was performed using a pan-BRAF antibody and a V600E mutation-specific antibody raised against an immunogenic synthetic peptide derived from the internal region of the BRAFV600E protein. BRAFV600E mutations in codon 15 were analyzed in extracted DNA using a multiplex, allele specific PCR–based assay. BRAF staining was scored independently by two pathologists blinded to mutation status. Results: In primary colon carcinomas stained with a pan-BRAF antibody, diffuse cytoplasmic staining for BRAF proteins was detected in 74 of 75 carcinomas with one case deemed non-evaluable. Using the mutation-specific BRAFV600E antibody, diffuse cytoplasmic staining was detected in 49 of 74 tumors without appreciable heterogeneity of expression. Among these 49 tumors expressing mutant BRAFV600E proteins, all (100%) were found to carry a BRAFV600E mutation according to a DNA-based assay. In contrast, absent BRAFV600E staining was observed in all 25 tumors that were found to have wild-type copies of BRAFV600E detected using a PCR-based assay. Conclusions: For the detection of mutant BRAFV600E, complete concordance was found between IHC and a DNA-based method in colon carcinomas. This finding supports the use of IHC as a simplified strategy to screen CRCs for mutant BRAFV600E proteins in routine clinical practice to inform clinical decision-making.

BACKGROUND: Several studies have reported what seem to be false-positive results using the Food and Drug Administration (FDA)–approved HercepTest (Dako Corp, Carpinteria, CA) to profile Her-2/neu amplification and overproduction in breast carcinoma. False-positive status has been based on comparisons with gene copy enumeration by fluorescence in situ hybridization (FISH) and with comparisons to immunohistochemistry (IMH) results using a monoclonal antibody. However, simple overexpression by tumor cells that have normal gene copy has not been evaluated by profiling mRNA expression, ie, such cases could simply represent true-positive, transcriptionally upregulated overexpression. MATERIALS AND METHODS: Four hundred infiltrating ductal carcinomas of breast were evaluated by IMH using monoclonal (CB11; Ventana Medical Systems, Inc, Tucson, AZ) and polyclonal (HercepTest; Dako) antibodies after antigen retrieval (AR). A polyclonal antibody sans AR (PCA/SAR) was also used. All IMH stains were evaluated and scored according to the guidelines for the FDA-approved HercepTest. A total of 145 of 400 carcinomas were subsequently evaluated by direct and digoxigenin-labeled (Dig) FISH, and 144 of 400 were evaluated by detection of mRNA overexpression via autoradiographic RNA:RNA in situ hybridization. RESULTS: Overall HercepTest/CB11 IMH discordance was 12%. Expression of mRNA was highly concordant with FISH and DigFISH amplification and with CB11 and PCA/SAR immunohistology. IMH false-positive cases (no Her-2/neu gene amplification) occurred with both HercepTest (23%) and CB11 (17%), and the majority of false-positive results (34 of 44) were scored as 2+. All 2+ false-positive cases were mRNA-negative. Combined results of HercepTest and CB11 showed that 79% (38 of 48) of 3+ cases were Her-2/neu gene amplified, but only 17% (seven of 41) of 2+ cases had increased gene copy. CONCLUSION: Discordant HercepTest/FISH results, and to a lesser extent discordance with CB11 IMH, are most commonly false-positive results with a score of 2+. The 2+ score as defined in the guidelines for the FDA-approved HercepTest should not be used as a criterion for trastuzumab therapy unless confirmed by FISH. Determination of Her-2 gene copy number by FISH may be a more accurate and reliable method for selecting patients eligible for trastuzumab therapy.

BACKGROUNDA point mutation (V600E) in the BRAF oncogene is a prognostic biomarker and may predict for nonresponse to anti‐EGFR antibody therapy in patients with colorectal carcinoma. BRAFV600E mutations are frequently detected in tumors with microsatellite instability and indicate a sporadic origin. We used a mutation‐specific antibody to examine mutant BRAFV600E protein expression and its concordance with BRAFV600E mutation data.METHODSPrimary stage III colon carcinomas were analyzed for BRAFV600E mutations in exon 15, and 50 BRAFV600E mutation carriers and 25 wild‐type tumors were selected for analysis of BRAF proteins by immunohistochemistry (IHC). IHC was performed in archival tissue specimens using a pan‐BRAF antibody and a mutation‐specific antibody against BRAFV600E proteins. Staining was scored by 2 pathologists who were blinded to clinical and mutation data.RESULTSUsing a pan‐BRAF antibody, total BRAF protein expression was observed in the tumor cell cytoplasm in 74 of 75 colon carcinomas. A mutation‐specific antibody identified diffuse cytoplasmic staining of mutant BRAFV600E proteins in 49 of 74 cancers. Analysis using a polymerase chain reaction‐based assay revealed that all 49 of these cancers carried BRAFV600E mutations. In contrast, BRAFV600E staining was absent in all 25 tumors that carried wild‐type copies of BRAF.CONCLUSIONSA BRAF mutation‐specific (V600E) antibody detected tumors with BRAFV600E mutations and exhibited complete concordance with a DNA‐based method. These results support the use of IHC as a simplified strategy to screen colorectal cancers for BRAFV600E mutations in clinical practice. Cancer 2013;119:2765–2770. © 2013 American Cancer Society.