Detection of epidermal growth factor receptor (EGFR) exon 19 E746-A750 deletion and EGFR exon 21 point mutations in lung adenocarcinoma by immunohistochemistry: a comparative study to EGFR exons 19 and 21 mutations analysis using PCR followed by high-resolution melting and pyrosequencing

Activating mutations in the epidermal growth factor receptor (EGFR) gene in non-small cell lung cancer (NSCLC) with adenocarcinoma histology confers susceptibility to treatment with EGFR tyrosine kinase inhibitors (TKI). Analysis of these activating mutations is typically performed by molecular techniques including polymerase chain reaction (PCR) amplification followed by deoxyribonucleic acid (DNA) melting curve analysis and/or direct sequencing. Recently developed mutation-specific immunohistochemical stains for the L858R point mutation in exon 21 and an E746-A750 deletion in exon 19 of the EGFR gene may offer a fast, cost-effective alternative to molecular testing. In this study, EGFR exons 19 and 21 mutations were analyzed using EGFR E746-A750 del and EGFR L585R point mutation-specific antibodies and the results were compared with the exon 19 deletions and exon 21 L588R point mutation as detected by molecular testing. The findings demonstrate a high concordance rate (100% in 12 cases) between the two methodologies for EGFR exon 21 L585R point mutation but a low concordance rate (54% in 22 cases) for exon 19 deletions when using EGFR E746-A750 mutation-specific antibody compared to molecular testing. This low concordance rate between the two methods is due to the fact that EGFR exon 19 mutations include deletions other than E746-A750 as well as insertion/deletions that will not be covered by exon 19 E746-A750 del mutation-specific antibody. Despite this limitation, the current EGFR mutation-specific antibodies can prove useful as an alternative to molecular tests for exon 21 L585R mutations as well as a subset of EGFR exon 19 deletion mutations, particularly in cases with low percentage of tumor concentration and in decalcified tissue specimens that are not suitable for DNA-based molecular assays.