The Performance of an E746-A750del Mutation Specific EGFR Antibody in Non-Small Cell Lung Cancer Specimens
Ainura Kyshtoobayeva, Kenneth J Bloom. Clarient, A GE Healthcare Company, Aliso Viejo, CA
Background: Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related deaths worldwide. Two-thirds of patients present with advanced disease and have an average survival of less than 1 year with standard chemotherapy. Studies have demonstrated that exon 19 deletion or L858R substitution in the EGFR gene are the most powerful predictive biomarkers in patients treated with erlotinib or gefitinib. This has led to the recommendation that EGFR mutational status be evaluated prior to initiating chemotherapy. Currently mutational status is assessed by sequencing of the EGFR gene or allele specific PCR. Approximately half of all EGFR mutations harbor deletions in exon 19. We sought to assess the performance of a E746-A750del mutation specific EGFR antibody purported to identify cells harboring the exon 19 deletion.
Design: 100 formalin fixed embedded tissue sections, 50 harboring an exon 19 deletion and 50 assessed as non-mutated or harboring a mutation other than an exon 19 deletion were pulled from our archives. 4 micron sections were stained with a rabbit monoclonal E747-A750del mutation specific antibody, 6B6, (cell signaling, Danvers, MA) 1:300, following heat-induced epitope retrieval, 100o C, pH9, 20 minutes.
Results: 31 (62%) of the 50 tumors harboring an exon 19 deletion showed expression of the 6B6 antibody ranging from 1+ to 3+ intensity. The remaining 19 tumor showed no expression. All 50 tumors lacking an EGFR mutation or harboring a mutation other than an exon 19 deletion showed no expression of the 6B6 antibody.
Conclusions: The E746-A750del mutation specific EGFR antibody 6B6 identified 62% of the tumors harboring an exon 19 deletion and showed no expression in tumors lacking and EGFR mutation or harboring a mutation other than an exon 19 deletion. The poor sensitivity of this antibody limits its usefulness in replacing or supplementing mutational testing by sequencing or allele specific PCR.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 304, Tuesday Afternoon