Monitoring of plasma pro-GRP level during EGFR-TKI treatment.

Abstract

10604 Background: Lung cancers harboring mutations in the epidermal growth factor receptor gene (EGFR) respond to EGFR tyrosine kinase inhibitors (EGFR-TKI), but drug resistance invariably emerges. The major acquired mechanisms of resistance are the EGFR T790M mutation or MET gene amplification. Transformation from NSCLC into small-cell lung cancer (SCLC) has been recently identified in acquired resistance to EGFR-TKI. However, it is difficult to predict the transformation during EGFR-TKI treatment because obtaining serial and sufficient specimens for biopsy is difficult. Pro-gastrin-releasing peptide (Pro-GRP) is a specific and sensitive tumor marker for SCLC. We evaluated the plasma Pro-GRP levels in EGFR-mutant NSCLCs and determined whether plasma Pro-GRP levels could predict SCLC transformation in resistance to EGFR-TKI. Methods: From July 2008 to December 2011, 49 patients with EGFR-mutant NSCLC who received EGFR-TKI treatment were enrolled. Plasma was obtained from these patients before EGFR-TKI treatment and when EGFR-TKI treatment failed. Pro-GRP and CEA levels were measured and compared before and after treatment. Results: Patient characteristics for 49 patients (15 men, 34 women) were as follows: median age, 62 years (41–81 years); histology, 46 adenocarcinomas (AD) and 3 non-AD tumors; and EGFR mutation type, 25 exon 19 deletions and 24 exon 21 L858R. All 49 patients had received EGFR-TKI treatment (45 with gefitinib and 4 with erlotinib); the response to EGFR-TKI treatment was PR in 39 patients, SD in 7, PD in 2, and NE in 1. Positive rate of ProGRP and CEA at pre-EGFR-TKI treatment was 2.0% and 57.2% and that at post-EGFR-TKI treatment was 6.1% and 69.4%, respectively. In 3 of 49 patients, the Pro-GRP levels had increased after treatment, but the CEA level did not increase. Objective responses to cytotoxic chemotherapy were noted in all 3 patients after EGFR-TKI treatment. Conclusions: Monitoring of plasma Pro-GRP during EGFR-TKI treatment may be useful for early detection of SCLC transformation in resistance to EGFR-TKI.