A Study of ASP8273 in Epidermal Growth Factor Receptor (EGFR) Tyrosine Kinase Inhibitor-Naïve Patients With Non-Small Cell Lung Cancer Harboring EGFR Mutations

Inclusion Criteria: * Patients with Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1. * Patients with a histologically or cytologically confirmed diagnosis of Stage IIIB or IV NSCLC. * Patients confirmed to have the deletion of exon 19 (del ex19), L858R, G719X, or L861Q mutation among the EGFR activating mutations (patients at the study site who are documented to have any of the above-stated EGFR activating mutations can be enrolled in the study). * Patients with a life expectancy ≥ 12 weeks based on the principal investigator's/subinvestigator's judgment. * Patients who meet all of the following requirements for laboratory tests within 7 days before enrollment. When 2 or more test results for a single parameter are found within the specified period, the last data before enrollment should be used for assessment. * Neutrophil count: ≥ 1,500/mm3 * Platelet count: ≥ 75,000/mm3 * Hemoglobin: ≥ 9 g/dL * Serum creatinine: \< 1.5 mg/dL * Total bilirubin (TBL): \< 1.5 × the upper limit of normal (ULN) at the site (this does not apply to patients with Gilbert syndrome) * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT): \< 2.5 ×the ULN at the site * Patients who meet all the following requirements for prior treatment for NSCLC: * Patients who have not received previous treatment with EGFR-TKIs\*1 \*1: Erlotinib, gefitinib, afatinib, and EGFR-TKIs under clinical investigation (e.g.,neratinib, dacomitinib). EGFR-TKIs that can inhibit E…