Rare and complex mutations of epidermal growth factor receptor (EGFR) and efficacy of tyrosine kinase inhibitor (TKI) in patients with non-small cell lung cancer (NSCLC).

Abstract

7566 Background: Other than in-frame deletional mutation (MT) in exon 19 and Leu858Arg point MT in EGFR gene, there are many rare and complex MT. The purpose of this study was to investigate was to clarify the clinical significance of rare and complex MT, and the efficacy of EGFR TKI in these patients. Methods: Rare MTs were defined any MT other than deletional MT in exon 19, Leu858Arg in exon 21, and Thr790Met in exon 20. Complex MT was defined two different EGFR MTs co-occurring within the single tumor sample. We have analyzed consecutive database of NSCLC patients who were treated with either gefitinib or erlotinib at Seoul National University Hospital between Jan. 2002 and Dec. 2011. For analysis of EGFR MT, coding sequences from exon 18 to 21 were amplified by nested PCR and subjected to direct sequencing methods. Results: Among the 1,159 TKI treated patients, 301 patients had EGFR MT (177 patients (58.8%) with del-19, 104 patients (34.6%) with Leu858Arg, and 20 patients (6.6%) with rare MT). Twenty-three (7.6%) patients have complex MT, and 55 (18.3%) patients have Gln787Gln polymorphism particularly associated with Leu858Arg MT. Identified rare MT were follows; exon 18: Leu692Phe, Glu707Lys, Glu709Gly, Lys714Asn, Gly7Ala, Thr725Thr, exon 19: Ala755Asp Lys737Thr, exon 20: Val786Met, exon21: Ala871Gly, Gly873Gln, Leu833Val, Val834Leu, Arg836Cys, Pro848Leu, Ala859Thr, Leu861Gln. When categorizing 3 groups (group A: classic MT alone, group B: complex MT with classic + rare MT, group C: rare MT alone or complex MT with rare MTs), response rate (RR) to TKI was different between each groups (RR= 78.7% in group A vs. 69.2% in group B vs. 38.5% in group C, respectively, P < 0.001). Progression-free survival (PFS) was also poorer in rare MT (median PFS: 12.1 mo vs. 7.6 mo vs. 2.1 mo, respectively, P= 0.020,). Gln787Gln polymorphism of exon 21 was not associated with RR or PFS (P= 0.101, P= 146, respectively) Conclusions: In this large case series, NSCLC patients who harboring rare MT other than del-19 and Leu858Arg, does not seems response to EGFR TKI. However, complex MT with the classical MT showed similar treatment efficacy toward EGFR TKI with that of classical MT alone.