This study was designed to compare the efficacy and safety of I-DXd with treatment of physician's choice in participants with relapsed small cell lung cancer (SCLC).

The primary objective of this study is to assess whether treatment with I-DXd improves objective response rate (ORR) and prolongs overall survival (OS) compared with treatment of physician's choice among participants with relapsed SCLC.

The secondary objectives of the study are to further evaluate the efficacy/safety of I-DXd, health economics and outcome research measures (including patient reported outcomes), immunogenicity of I-DXd, B7-H3 protein expression, and characterize the pharmacokinetics of I-DXd.

Inclusion Criteria

Participants must meet all the following criteria to be eligible for randomization into the study:

1. Sign and date the informed consent form prior to the start of any study-specific qualification procedures.
2. Adults ≥18 years or the minimum legal adult age (whichever is greater) at the time the informed consent form is signed.
3. Has histologically or cytologically documented extensive-stage small cell lung cancer (ES-SCLC).
4. The participant must provide adequate baseline tumor samples with sufficient quantity and quality of tumor tissue content.
5. Has received prior therapy with only one prior platinum-based line as systemic therapy for SCLC with at least 2 cycles of therapy and a chemotherapy free-interval of ≥30 days.
6. Has at least 1 measurable lesion according to RECIST v1.1 as assessed by the investigator.
7. Has documentation of radiological disease progression on or after the most recent systemic therapy.
8. Has ECOG PS of ≤1 within 7 days prior to Cycle 1 Day 1 (C1D1).
9. Has no evidence of brain or leptomeningeal disease (spinal cord or central nervous system [CNS] metastases) based on history and physical examination. Subjects must require no treatment with steroids or anticonvulsants and have a stable neurologic status for at least 2 weeks prior to the first dose of study drug.

Exclusion Criteria

Participants who meet any of the following criteria will be disqualified from entering the study:

1. Has received prior treatment with orlotamab, enoblituzumab, or other B7 homologue 3 (B7-H3) targeted agents, including I-DXd.

2. Prior discontinuation of an antibody drug conjugate (ADC) that consists of an exatecan derivative (eg, trastuzumab deruxtecan) due to treatment-related toxicities.

3. Has received any of the comparators used in this study or any topoisomerase I inhibitor.

4. Has inadequate washout period before randomization as specified in the protocol.

5. Has any of the following conditions within the past 6 months: cerebrovascular accident, transient ischemic attack, or another arterial thromboembolic event.

6. Has uncontrolled or significant cardiovascular disease.

7. Has clinically significant corneal disease.

8. Has any history of ILD/pneumonitis irrespective of steroid use, or current ILD, or suspected ILD, or ILD that cannot be ruled out by imaging at Screening. Participants may be eligible if they had history of radiation pneumonitis that did not require steroids.

   Examples of suspected ILD/pneumonitis by imaging include the presence of lung parenchymal fibrosis, such as combined pulmonary fibrosis and emphysema (CPFE) and any radiographic features consistent with ILA, including but not limited to, extensive ground glass opacities, reticular opacities, traction bronchiectasis, and honeycombing.

9. Has clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses, including, but not limited to, any underlying pulmonary disorder and potential pulmonary involvement caused by any autoimmune, connective tissue, or inflammatory disorders, prior pneumonectomy, or requirement for supplemental oxygen.

De-identified individual participant data (IPD) on completed studies 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/

Completed studies that has reached a global end or completion with all data set collected and analyzed, and 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 on completed 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