This study was designed to evaluate the safety and efficacy of trastuzumab deruxtecan in HER2-mutated metastatic non-small cell lung cancer (NSCLC) participants who had disease recurrence or progression during/after at least one regimen of prior anticancer therapy (second line or later) that must have contained a platinum-based chemotherapy drug.

This randomized, two-arm, phase 2, multicenter study will evaluate the safety and efficacy of 5.4 mg/kg and 6.4 mg/kg trastuzumab deruxtecan administered every 3 weeks (Q3W) in participants with HER2-mutated metastatic NSCLC. Each participant is expected to receive approximately 14 months of trastuzumab deruxtecan treatment. The primary endpoint of the study will be confirmed objective response rate (blinded independent central review). Secondary endpoints will include, but not limited to, disease control rate, duration of response, progression-free survival, objective response rate (investigator), overall survival, and safety.

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 including platinum therapy in the metastatic/locally advanced setting and not amenable to curative surgery or radiation. Participant must have progressed during or after the last treatment regimen or discontinued because of unacceptable toxicity.
• 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. Resection and core needle biopsy are acceptable. Fine needle aspirates or cell block are not acceptable.
• Eastern Cooperative Oncology Group performance status 0 to 1
• Left ventricular ejection fraction ≥ 50% within 28 days before randomization Resection and core needle biopsy are acceptable - 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), BRAF, or MET exon 14 gene or a known anaplastic lymphoma kinase (ALK), ROS1, RET, or NTRK 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 randomization 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) such as those with serologic evidence of viral infection within 28 days of Cycle 1, Day 1
• 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
• Had prior treatment with any agent, including an antibody drug conjugate (ADC), containing a chemotherapeutic agent targeting topoisomerase I

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.