Studies at RP2D Cohort 1: Patients may have de novo T790M mutation, but it is not required. Cohort 2 and Cohort 3: Patients must have EGRFm (del 19 AND T790M or L858R AND T790M) NSCLC tumors as detected by local EGFR mutation test that includes QIAGEN Therascreen EGFR RGQ PCR kit, Roche cobas® EGFR Mutation Test or a sponsor-approved laboratory developed test that is validated in a CLIA laboratory, which will then be retrospectively confirmed by the central validated Thermo Fisher Scientific Oncomine Next Generation Sequencing (NGS) cancer panel test. Patients will also be enrolled if they solely test positive for EGFR (del 19 AND T790M or L858R AND T790M) NSCLC in plasma detected by local EGFR mutation test that includes QIAGEN Therascreen EGFR Plasma RGQ kit, Roche cobas® EGFR mutation test v2 (US-IVD) or Sysmex Inostic's OncoBEAMTM EGFR test or a sponsor-approved laboratory developed test that is validated in a CLIA laboratory, which will then be retrospectively confirmed by a validated cfDNA test as determined by the Sponsor.