EGFR mutation and intron 1 CA repeat polymorphism as predictive markers of gefitinib responsiveness in non-small cell lung cancer (NSCLC)

Abstract

7173 Background: EGFR mutation is significantly associated with objective response and prolonged survival in NSCLC patients treated with gefitinib. However, presence of mutant nonresponses and nonmutant responses mandates investigation of other molecular markers for more effective prediction of gefitinib sensitivity in NSCLC. It is unclear whether low CA repeat number in EGFR intron 1 has such a predictive role. Methods: Advanced NSCLC patients received gefitinib 250mg/day. EGFR mutation in exons 18 - 21 were identified by direct sequencing of PCR products of DNA extracted from archival paraffin embedded tissue. Number of CA repeat in intron 1 of EGFR was determined by GeneScan with tumoral DNA. Baseline characteristics, mutational status, CA repeat number and efficacy of gefitinib were analyzed in respect to each other. Results: To date, 73 patients were evaluable for EGFR mutation, CA repeat and gefitinib responsiveness. 14 patients (19.2%) harbored EGFR mutation (7 deletion in exon 19, 4 L858R, 1 L861Q, 1 G719A, and 1 insertion in exon 20). Most common CA repeat genotype was 20/20 repeat (31 patients) followed by 16/20 repeat (15 patients). Patients were classified as having either low CA repeat (sum of both allele ≤ 37 repeats) or high CA repeat (≥ 38 repeats). 34 patients (46.6%) had low repeat, whereas 39 patients (53.4%) had high repeat. Patients with EGFR mutation showed better objective response (response rate [RR] 57.1% vs. 10.2% in wild type [WT], p < 0.001), time-to-progression (TTP) (p = 0.031, median 5.1 vs. 1.9 months in WT), and overall survival (OS) (p = 0.051, median14.5 vs. 7.4 months in WT). In the whole study population, low CA repeat was not associated with RR (p = 0.38), TTP (p = 0.15), or OS (p = 0.51). However, in the 59 patients without an EGFR mutation, patients with low CA repeat tended to have better objective response (RR 17.2% [5/29] in low repeat vs. 3.3% [1/30] in high repeat, p = 0.10) and significantly better TTP (p = 0.019, median 2.2 months in low repeat vs. 1.2 months in high repeat). Conclusions: Our results suggest that low number of CA repeats in EGFR intron 1 may have possible role in prediction of gefitinib responsiveness when analyzed together with EGFR mutational status. [Table: see text]