Immunohistochemistry with a novel mutation-specific monoclonal antibody as a screening tool for the EGFR L858R mutational status in primary lung adenocarcinoma.

Epidermal growth factor receptor (EGFR) mutation status is the best predictor of patient response to treatments with tyrosine kinase inhibitors in primary lung adenocarcinoma and is typically analyzed by DNA-based techniques, such as direct DNA sequencing and allele-specific PCR. Recently, however, two mutation-specific antibodies against delE746-A750 in exon 19 and L858R in exon 21 have opened the door for a more convenient and more efficient strategy to determine EGFR mutation status. To evaluate the clinical application of a new mutation-specific mouse monoclonal antibody for EGFR (L858R), we performed immunohistochemistry (IHC) studies with tumor samples from primary lung adenocarcinoma in retrospective and validation settings. A total of 215 cases of primary lung adenocarcinoma were examined and compared using a combination of DNA-based techniques (direct DNA sequencing and/or allele-specific PCR) and protein-based IHC. IHC staining was assessed on a 0 to 3+ score scale, and a cutoff value of 2+ was used as positive by IHC. In the retrospective setting, statistical analyses of the data showed that the sensitivity of IHC was 90.9% and the specificity was 96.8%. Findings from the validation study demonstrated that the sensitivity and specificity of IHC were 88.2% and 100%, respectively. IHC with the novel mutation-specific antibody could be used as a screening method to assess the EGFR L858R mutation status in primary lung adenocarcinoma.