Inclusion Criteria:

          -  Written informed consent

          -  Men or women ≥18 years, follow local regulatory requirements if the legal age of the
             consent for study participation is >18 years

          -  Pathologically documented metastatic NSCLC with a known activating HER2 mutation.
             Note: A HER2 mutation documented only from a liquid biopsy samples cannot be used for
             enrollment.

          -  Had previous treatment (second line or later [2L+], including platinum therapy), not
             amenable to curative surgery or radiation

          -  Presence of at least 1 measurable lesion confirmed by the blinded Independent Central
             Review based on RECIST version 1.1

          -  Willing and able to provide an archival tumor tissue sample. A fresh biopsy is
             required if an archival tumor tissue sample cannot be supplied. Fine needle aspirates
             are not acceptable.

          -  Eastern Cooperative Oncology Group performance status 0 to 1

          -  Left ventricular ejection fraction ≥ 50% within 28 days before randomization

          -  Adequate organ function as specified in protocol within 14 days before randomization

          -  Adequate treatment washout period before randomization

          -  Participants of reproductive/childbearing potential agree to use a highly effective
             form of contraception (or avoid intercourse) during study period and up to 7 months
             (females) and 4 months (males) after last study dose

          -  Males should not freeze or donate sperm throughout the study period up to at least 4
             months after last study dose; females should not donate or retrieve ova for their own
             use throughout the study period and up to at least 7 months after last study dose

          -  Life expectancy 3 months or more

        Exclusion Criteria:

          -  Known driver mutation in the epidermal growth factor receptor (EGFR) or BRAF gene or a
             known anaplastic lymphoma kinase (ALK) or ROS1 fusion

          -  Medical history of myocardial infarction within 6 months before randomization,
             symptomatic congestive heart failure (CHF) (New York Heart Association Class II to
             IV). Participants with troponin levels above upper limit of normal at screening (as
             defined by the manufacturer) and without any myocardial infarction (MI)-related
             symptoms should have a cardiologic consultation before enrollment to rule out MI

          -  Corrected QT interval (QTcF) prolongation > 470 msec (females) or >450 msec (males)
             based on average of the triplicate12-lead electrocardiogram at screening

          -  History of non-infectious interstitial lung disease (ILD)/pneumonitis that required
             steroids, current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled
             out by imaging at screening

          -  Spinal cord compression or clinically active central nervous system metastases,
             defined as untreated and symptomatic, or requiring therapy with corticosteroids or
             anticonvulsants to control associated symptoms

          -  Multiple primary malignancies within 3 years, except adequately resected non-melanoma
             skin cancer, curatively treated in-situ disease, or other solid tumors curatively
             treated

          -  History of severe hypersensitivity reactions to either the drug substances or inactive
             ingredients in the drug product

          -  History of severe hypersensitivity reactions to other monoclonal antibodies

          -  Uncontrolled infection requiring IV antibiotics, antivirals, or antifungals

          -  Substance abuse or any other medical conditions such as clinically significant cardiac
             or psychological conditions, that may, in the opinion of the investigator, interfere
             with the participant's participation in the clinical study or evaluation of the
             clinical study results

          -  Known human immunodeficiency virus (HIV) infection

          -  Known active, clinically relevant liver disease (eg, active hepatitis B, or active
             hepatitis C), based on available blood tests, liver ultrasound, or liver biopsy
             results

          -  Unresolved toxicities from previous anticancer therapy, defined as toxicities (other
             than alopecia) not yet resolved to Grade ≤ 1 or baseline

          -  Pregnant, breastfeeding, or planning to become pregnant

          -  Otherwise considered inappropriate for the study by the Investigator

          -  Lung-specific intercurrent clinically significant illnesses including, but not limited
             to, any underlying pulmonary disorder (eg. pulmonary emboli within three months of the
             study randomization, severe asthma, severe COPD, restrictive lung disease, pleural
             effusion, etc.)

          -  Any autoimmune, connective tissue or inflammatory disorders (e.g., Rheumatoid
             arthritis, Sjogren's, sarcoidosis etc.) where there is documented, or a suspicion of
             pulmonary involvement at the time of screening

          -  Prior complete pneumonectomy