• Subjects age 18 or above (19 or above for South Korea)

• Subjects with pathologically confirmed and finally diagnosed advanced and/or metastatic NSCLC with active EGFR mutant

• Subjects who show disease progression after receiving standard anticancer therapy, including approved EGFR-TKI therapeutic and/or up to 1 time of platinum-based anticancer chemotherapy. For the Part C dose expansion phase, approved EGFR-TKI with activity against T790M mutant such as Osimertinib must be included.

• Subjects with a test result of locally confirmed EGFR mutant obtained through a test method approved by the sponsor using either a tumor tissue and/or plasma ctDNA. It is preferred that samples used for analysis are collected during or after disease progression from the last EGFR-TKI administration. If there is a sample retained after disease progression from prior therapy, it may be submitted.

∙ Part A dose escalation and Part B exploration studies: Advanced NSCLC subjects who are positive to EGFR mutant C797S or T790M

‣ Part C dose expansion study: Advanced NSCLC subjects who are positive for EGFR mutations C797S and T790M in Cohort 1, those who are positive for C797S and negative for T790M in Cohort 2, those who are negative for C797S and positive for T790M in Cohort 3, subjects who are positive for any EGFR mutations and stable brain metastasis in Cohort 4, and those who have any EGFR dependent mutations other than C797S or T790M in Cohort 5.

• For Part C, subjects with at least 1 measurable lesion that has not been previously radiated as defined by RECIST version 1.1

• Subjects with ECOG performance status 0 or 1

• Acute effect from a previous therapy that recovers to the baseline severity or ≤ Common Terminology Criteria for Adverse Events (CTCAE) grade 1, except for an AE not corresponding to a safety risk, as determined by the investigator based on discussion with the sponsor. Note: A chronic condition not expected to recover (≤ grade 2, e.g. neuropathy, myalgia, alopecia) is an exception, and a subject with such a condition can be enrolled.

• Appropriate bone marrow and organ functions, including the following:

∙ Hemoglobin ≥ 9.0 g/dL

‣ Platelet ≥ 75 × 109/L

‣ Absolute neutrophil count ≥ 1.0 × 109/L

‣ Serum Total Bilirubin (TBL) ≤ 1.5 × Upper Limit of Normal Range (ULN) (≤ 3.0 x ULN for a subject with documented Gilbert syndrome)

‣ Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) ≤ 3.0 ×ULN, or if there is a hepatic metastasis caused by tumor, ≤ 5.0 × ULN

‣ \*Estimated creatinine clearance calculated using the Cockcroft-Gault formula to ≥ 60 mL/min/1.73m2

• CrCl (male) = (\[140 - age\] × weight (kg)) / (serum creatinine (mg/dL) × 72), CrCl (female) = CrCl (male) ×0.85

• For women with childbearing potential

∙ The serum pregnancy test result must be negative before screening and the first dose of the investigational product

‣ Women of childbearing potential who are sexually active with a non-sterilized male partner must use at least 1 or more effective contraceptive methods from the first dose of the investigational product to 90 days after the last dose

∙ \*Progesterone hormone contraceptive inhibiting ovulation, including an oral, injectable and implant type, intrauterine device, bilateral tubal ligation, use of spermicide or condom by the male partner, etc.

‣ Must not breastfeed during the study and up to 90 days after the last dose of the investigational product

⁃ Male subjects who are sexually active with a non-sterilized female partner of childbearing potential must agree to using an effective contraceptive method (spermicide, condom, etc.) from the first dose of the investigational product to 90 days after the last dose and not donating their sperms