Inclusion Criteria:

        Inclusion Criteria Specific to Dose Escalation and Second-Line Dose Expansion:

          -  Documentation of EGFR exon 19 deletion or L858R mutation detected from tumor tissue

          -  Must have received osimertinib for locally advanced or metastatic disease at a dose of
             80 mg once daily (QD) for at least 6 weeks and must not miss more than two doses
             during the 2 weeks prior to the first day of study treatment (Cycle 1, Day 1)

          -  Must not have received any other prior systemic cancer therapies in the locally
             advanced/metastatic setting

          -  Has documentation of radiological disease progression following first-line treatment
             with osimertinib in the locally advanced or metastatic setting

        Inclusion Criteria Specific to First-line Dose Expansion:

          -  The tumor tissue harbors one of the 2 common EGFR mutations occurring in NSCLC known
             to be associated with EGFR-TKI sensitivity (exon 19 deletion or L858R) as assessed by
             Clinical Laboratory Improvement Amendments (CLIA)-certified (United States [US]
             sites), accredited (outside of the US), local laboratory or central laboratory. Only
             tissue-based testing will be accepted.

          -  Participants must have previously untreated locally advanced or metastatic NSCLC and
             must be eligible to receive first-line treatment with osimertinib, according to the
             judgment of the investigator. Prior adjuvant or neo-adjuvant therapy (chemotherapy,
             radiotherapy, investigational agents; except with osimertinib) is permitted.

        All Participants:

        Participants must meet all criteria to be eligible for inclusion in this study:

          -  Histologically or cytologically documented locally advanced or metastatic NSCLC not
             amenable to curative surgery or radiation.

          -  At least 1 measurable lesion as assessed by Investigator as per Response Evaluation
             Criteria in Solid Tumors (RECIST v1.1)

          -  Willing to provide required tumor tissue of sufficient quantity (as defined in the
             laboratory manual) and contain adequate tumor tissue content (as confirmed by
             hematoxylin and eosin (H&E) staining at central laboratory). Required tumor tissue can
             be provided as either:

               -  Pre-treatment tumor biopsy from at least 1 lesion not previously irradiated and
                  amenable to core biopsy OR

               -  Archival tissue collected from a biopsy performed within 3 months prior to
                  signing of the tissue consent and since progression while on the most recent
                  cancer therapy regimen.

               -  On-study tumor biopsies are required for the first 15 participants in Dose
                  Escalation.

          -  Has adequate bone marrow reserve and organ function based on local laboratory data
             within 14 days prior to Cycle 1, Day 1 (Dose Escalation and First-Line Dose Expansion)
             or within 14 days prior to randomization (Second-Line Dose Expansion):

               -  Platelet count: ≥100 000/mm^3 or ≥100 × 10^9/L (platelet transfusions are not
                  allowed up to 14 days prior to Cycle 1, Day 1 to meet eligibility)

               -  Hemoglobin: ≥9.0 g/dL (transfusion and/or growth factor support is allowed)

               -  Absolute neutrophil count ; 1500/mm^3 or ≥1.5 × 10^9/L

               -  Serum creatinine (SCr) OR creatinine clearance (CrCl): SCr ≤1.5 × ULN, OR CrCl
                  ≥30 mL/min as calculated using the Cockcroft-Gault equation or measured CrCl;
                  confirmation of CrCl is only required when creatinine is >1.5 × ULN

          -  Aspartate aminotransferase/ alanine aminotransferase: ≤3 × ULN (if liver metastases
             are present, ≤5 × ULN)

          -  Total bilirubin: ≤1.5 × ULN if no liver metastases (<3 × ULN in the presence of
             documented Gilbert's syndrome [unconjugated hyperbilirubinemia] or liver metastases)

          -  Serum albumin ; ≥2.5 g/dL

          -  Prothrombin time (PT) or PT-international normalized ratio (INR) and Activated partial
             thromboplastin time (aPTT) / Partial thromboplastin time (PTT): ≤1.5 × ULN, except for
             subjects on coumarin-derivative anticoagulants or other similar anticoagulant therapy,
             who must have PT-INR within therapeutic range as deemed appropriate by the
             Investigator.

        Exclusion Criteria:

          -  Any previous histologic or cytologic evidence of small cell OR combined small
             cell/non-small cell disease in the archival tumor tissue or pretreatment tumor biopsy.

          -  Any history of interstitial lung disease (including pulmonary fibrosis or radiation
             pneumonitis), has current interstitial lung disease (ILD), or is suspected to have
             such disease by imaging during screening.

          -  Clinically severe pulmonary compromise (based on Investigator's assessment) resulting
             from intercurrent pulmonary illnesses including, but not limited to:

               -  Any underlying pulmonary disorder (eg, pulmonary emboli within three months of
                  the study enrollment or randomization, severe asthma, severe chronic obstructive
                  pulmonary disease, restrictive lung disease, pleural effusion);

               -  Any autoimmune, connective tissue or inflammatory disorders with pulmonary
                  involvement (eg, rheumatoid arthritis, Sjogren's syndrome, sarcoidosis); OR prior
                  complete pneumonectomy.

          -  Is receiving chronic systemic corticosteroids dosed at >10 mg prednisone or equivalent
             anti-inflammatory activity or any form of immunosuppressive therapy prior to Cycle 1,
             Day 1 (Dose Escalation and First-Line Dose Expansion) or prior to randomization
             (Second-Line Dose Expansion). Participants who require use of bronchodilators, inhaled
             or topical steroids, or local steroid injections may be included in the study.

          -  Evidence of any leptomeningeal disease.

          -  Evidence of clinically active spinal cord compression or brain metastases, defined as
             untreated and symptomatic, or requiring therapy with corticosteroids or
             anticonvulsants to control associated symptoms. Participants with clinically inactive
             or treated brain metastases who are asymptomatic (ie, without neurologic signs or
             symptoms and do not require treatment with corticosteroids or anticonvulsants) may be
             included in the study.

          -  Inadequate washout period prior to Cycle 1, Day 1 (Dose Escalation and First-Line Dose
             Expansion) or prior to randomization (Second-Line Dose Expansion) defined as:

               -  Whole brain radiation therapy <14 days or stereotactic brain radiation therapy <7
                  days;

               -  Any systemic anticancer (excluding osimertinib in all Dose Escalation Cohorts and
                  in Second-Line Dose Expansion [Arms 1, 2, and 1b]), including investigational
                  agents, <14 days or 5 half-lives, whichever is longer

               -  Immune checkpoint inhibitor therapy <5 half-lives

               -  Major surgery (excluding placement of vascular access) <4 weeks

               -  Radiotherapy treatment to more than 30% of the bone marrow or with a wide field
                  of radiation < 28 days or palliative radiation therapy <14 days

               -  Chloroquine or hydroxychloroquine ≤14 days

               -  Medications or herbal supplemented known to be strong inducers of cytochrome P450
                  (CYP) 3A4 <21 days.

          -  Has unresolved toxicities from previous anticancer therapy, defined as toxicities
             (other than alopecia) not yet resolved to National Cancer Institute Common Terminology
             Criteria for Adverse Events (NCI-CTCAE) version 5.0, Grade ≤1 or baseline. Subjects
             with chronic Grade 2 toxicities may be eligible per the discretion of the Investigator
             after consultation with the Sponsor Medical Monitor or designee.

          -  Refractory nausea and vomiting, chronic gastrointestinal diseases, inability to
             swallow osimertinib, or previous significant bowel resection that would preclude
             adequate absorption of osimertinib.

          -  Has any primary malignancy other than locally advanced or metastatic NSCLC within 3
             years prior to Cycle 1, Day 1 (Dose Escalation and First-Line Dose Expansion) or
             within 3 years prior to randomization (Second-Line Dose Expansion), except adequately
             resected non-melanoma skin cancer, curatively treated in situ disease, or other solid
             tumors curatively treated.

          -  Uncontrolled or significant cardiovascular disease prior to Cycle 1, Day 1 (Dose
             Escalation and First-Line Dose Expansion) or prior to randomization (Second-Line Dose
             Expansion) including:

               -  Mean corrected QT interval using Fridericia's formula (QTcF) prolongation
                  interval of >470 ms for females and >450 ms for males in 3 successive screening
                  measurements

               -  Left ventricular ejection fraction (LVEF) <50% by either echocardiogram (ECHO) or
                  multigated acquisition (MUGA) scan

               -  Resting systolic blood pressure >180 mmHg or diastolic blood pressure >110 mmHg

               -  Myocardial infarction within 6 months

               -  New York Heart Association (NYHA) Classes 2 to 4 congestive heart failure within
                  28 days

               -  Uncontrolled angina pectoris within 6 months

               -  Has cardiac arrhythmia requiring antiarrhythmic treatment

               -  Complete left or right bundle branch block within 6 months

               -  History of second- or third-degree heart block or PR interval >250 ms within 6
                  months

               -  History of clinically relevant ventricular arrhythmias, such as ventricular
                  tachycardia, ventricular fibrillation, or Torsade de Pointes

               -  Has any factors that increase the risk of corrected QT (QTc) prolongation or risk
                  of arrhythmic events, such as heart failure, hypokalemia, congenital long QT
                  syndrome, family history of long QT syndrome, or unexplained sudden death under
                  40 years of age in first-degree relatives, or any concomitant medication known to
                  prolong the QT interval

          -  Has clinically significant corneal disease

          -  Any evidence of severe or uncontrolled diseases including active bleeding diatheses,
             active infection, psychiatric illness/social situations, geographical factors,
             substance abuse, or other factors which in the Investigator's opinion makes it
             undesirable for the subject to participate in the study or which would jeopardize
             compliance with the protocol. Screening for chronic conditions is not required.