DS-8201a in Human Epidermal Growth Factor Receptor 2 (HER2)-Expressing or -Mutated Non-Small Cell Lung Cancer

Inclusion Criteria:

Age ≥20 years old in Japan, ≥18 years old in other countries
Pathologically documented unresectable and/or metastatic non-squamous NSCLC
Has relapsed from or is refractory to standard treatment or for which no standard treatment is available
For Cohort 1 and Cohort 1a: HER2-overexpression (IHC 2+ or 3+) status must be assessed and confirmed by Clinical Laboratory Improvement Amendments (CLIA)-certified laboratory or equivalent, from an archival tumor tissue sample
For Cohort 2 only: Participant has any known documented activating HER2 mutation from an archival tumor tissue sample analyzed by CLIA laboratory or equivalent. Note: HER2 mutation documented only from a liquid biopsy sample cannot be used for enrollment.
Presence of at least 1 measurable lesion assessed by the investigator and based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1
Is willing and able to provide an adequate archival tumor tissue sample
Is willing to undergo a tissue biopsy, after the completion of the most recent treatment regimen
Has Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 1

Exclusion Criteria:

Had been previously treated with HER2-targeted therapies, except for pan-HER class tyrosine kinase inhibitors
For Cohort 1 and Cohort 1a: Has known HER2 mutation
Has a medical history of myocardial infarction, symptomatic congestive heart failure (CHF) (NYHA classes II-IV), unstable angina or serious cardiac arrhythmia
Has a history of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required steroids, or current ILD/pneumonitis, or suspected ILD/pneumonitis that cannot be ruled out due to imaging at screening
Has a QT interval corrected by Fridericia's formula (QTcF) prolongation to > 450 millisecond (ms) in males and > 470 ms in females
Has a medical history of clinically significant lung disease
Is suspected to have certain other protocol-defined diseases based on imaging at screening period

Has history of any disease, metastatic condition, drug/medication use or other condition that might, per protocol or in the opinion of the investigator, compromise:

safety or well-being of the participant or offspring
safety of study staff
analysis of results