Immunohistochemical Screening Using Egfr Mutation-Specific Antibodies in Lung Adenocarcinomas: Diamond Project

Abstract

ABSTRACT Aim: Epidermal growth factor receptor (EGFR) mutations is the single most important predictor of clinical response and outcome using EGFR tyrosine kinase inhibitors (TKI) in lung adenocarcinomas. The most common gene alterations are EGFR deletions involving exon 19 and L858R point mutation in exon 21. We evaluated the accuracy of EGFR mutation-specific antibodies in different cytology and histologic samples. Methods: A series of 111 lung adenocarcinomas diagnosed on cytology (21 cases), biopsy (58) and surgical resections (32) were selected; all cases were previously investigated by Sanger sequencing and/or pyrosequencing (EGFR-KRAS mutation) and by immunohistochemistry(IHC)/FISH (ALK status). IHC using EGFR mutation-specific antibodies were tested using an automated immunostainer. Cases were quoted as positive when at least 2+ staining was present in at least 5% of tumor cells. Results: Conventional molecular analyses showed EGFR mutations in 52 cases (47%), KRAS mutations in 44 cases (40%), ALK positivity in 5 cases (4%) and triple negative setup in 10 cases. There were 19 and 25 tumors harboring L858R and delE746-A750, respectively, while 4 cases had uncommon mutations in exon 19, 2 cases harbor L861Q in exon 21, 2 T790M in exon 20, G719G and G719A in exon 18. At IHC, overall sensitivity was 76.5% and specificity was 98.3%. The sensitivity and specificity of antibodies for exon 19 was 68% and 100%, respectively, for exon 21 was 91% and 99%. Sensitivity and specificity in non-EGFR mutated tumors was absolute (100%). No significant difference in sensitivity and specificity was observed when results were statistically matched with different types of samples. Conclusions: The EGFR mutation-specific antibodies have a high specificity and fair-to-high sensitivity in classic EGFR mutations, while they do not recognized uncommon EGFR mutations, but no cross-reaction with tumors harboring different molecular settings was evidenced. The antibodies work equally well on biopsies and cytology, permitting a useful and rapid screening in cases with poor material. Negative results do not permit to robustly exclude the presence of EGFR mutations, requiring further molecular analysis, possibly microdissecting the same slides tested at IHC. Disclosure: All authors have declared no conflicts of interest.