Abstract 760: Detection of EGFR T790M mutation by ddPCR in untreated NSCLC patients: Correlation with clinical outcome

Abstract

Abstract Background: Activating EGFR mutations are associated with response to first generation tyrosine kinase inhibitors (TKI) that significantly increased PFS and OS in NSCLC patients. However, almost invariably, patients relapse while in treatment with TKI, mostly for the presence of EGFR T790M mutation. New second and third generation EGFR inhibitors active against T790M are now under development with very promising results. To date it is not known if the presence of T790M (and its amount) at diagnosis influences clinical outcome of patients with activating EGFR mutation. Methods: We analysed 50 cases with NSCLC. 48 patients harbour TKI sensitizing mutation in either exon 19 (N=24) or 21 (N=19). 2 EGFR wt patients (blinded to the investigator) were analysed in parallel. These patients were screened by ddPCR for the presence of T790M mutation using Biorad QX200 Droplet Digital PCR System. We used rough DNA extract from FFPE sections after deparaffinization and proteinase K digestion, as available in pathology unit for daily diagnosis. Results: 12 samples failed to amplify, maybe due to the poor quality of DNA. 13 samples produced results, but were excluded for the analysis because of too low number of calls retrieved. T790M mutation was detected in a significant proportion of remaining cases. Among the latter, 4 patients were sampled after TKI treatment and here the percentage of T790M were higher compared to those patients not treated [0.65% - 28% vs 0.019% - 1.65%, respectively]. One out four of these patients was not detected by routinely method of sequencing (Sanger or RT-PCR). T790M positive samples harboured mutations affecting exon 19 or 21 in equal manner. Conclusions: ddPCR has proven to be a sensitive method to detect T790M mutation, although the quality of DNA could affect the results. The system has been challenged for specificity an sensitivity and the results proved to be clinically relevant. The correlation between the T790M positivity and clinical outcome will be available and we plan to define a ddPCR threshold value which can help in selecting those patients who are likely to have early recurrence under first generation TKI and that could therefore be directly shifted to second or third generation inhibitors. Citation Format: Monica Ganzinelli, Eliana Rulli, Elena Tamborini, Adele Busico, Giuseppe Lo Russo, Giulia Corrao, Milena Vitali, Marina Chiara Garassino, Massimo Broggini, Mirko Marabese. Detection of EGFR T790M mutation by ddPCR in untreated NSCLC patients: Correlation with clinical outcome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 760. doi:10.1158/1538-7445.AM2017-760