Noninvasive Detection of EGFR T790M in Gefitinib or Erlotinib Resistant Non-Small Cell Lung Cancer

Purpose: Tumors from 50% of epidermal growth factor receptor (EGFR) mutant non - small cell lung cancer patients that develop resistance to gefitinib or erlotinib will contain a secondary EGFR T790M mutation. As most patients do not undergo repeated tumor biopsies we evaluated whether EGFR T790M could be detected using plasma DNA. Experimental Design: DNA from plasma of 54 patients with known clinical response to gefitinib or erlotinib was extracted and used to detect both EGFR-activating and EGFR T790M mutations. Forty-three (80%) of patients had tumor EGFR sequencing (EGFR mutant/wild type: 30/13) and seven patients also had EGFR T790M gefitinib/erlotinib-resistant tumors. EGFR mutations were detected using two methods, the Scorpion Amplification Refractory Mutation System and the WAVE/Surveyor, combined with whole genome amplification. Results: Both EGFR-activating and EGFR T790M were identified in 70% of patients with known tumor EGFR-activating (21 of 30) or T790M (5 of 7) mutations. EGFR T790M was identified from plasma DNA in 54% (15 of 28) of patients with prior clinical response to gefitinib/erlotinib, 29% (4 of 14) with prior stable disease, and in 0% (0 of 12) that had primary progressive disease or were untreated with gefitinib/erlotinib. Conclusions: EGFR T790M can be detected using plasma DNA from gefitinib- or erlotinib-resistant patients. This noninvasive method may aid in monitoring drug resistance and in directing the course of subsequent therapy.