• Male/female participants who are at least 18 years of age on the day of signing informed consent with histologically or cytologically confirmed diagnosis of ES SCLC will be enrolled in this study.

• The participant has not been previously treated with systemic therapy for ES SCLC (i.e., the disease is treatment naïve).

• Note: Participants previously treated for limited SCLC will be allowed with disease-free survival (DFS) of 6 months after completion of all treatment.

• Participants who have AEs due to previous anticancer therapies must have recovered to ≤Grade 1 or baseline. Participants with endocrine-related AEs who are adequately treated with hormone replacement or participants who have ≤Grade 2 neuropathy are eligible.

• The participant (or legally acceptable representative if applicable) provides written informed consent for the trial.

• Has measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions.

• Archival tumor tissue sample or newly obtained \[core, incisional or excisional\] biopsy of a tumor lesion not previously irradiated has been provided. Note: Participants with asymptomatic brain metastases will be eligible. Formalin-fixed, paraffin embedded (FFPE) tissue blocks are preferred to slides. Newly obtained biopsies are preferred to archived tissue.

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Evaluation of ECOG is to be performed within 3 days prior to the first dose of study intervention.

• Life expectancy \>3 months.

• Has adequate organ function as defined in the following table (Table 2). Specimens must be collected within 10 days prior to the start of study intervention.

⁃ A female participant is eligible to participate if she is not pregnant (refer to the Clinical Trials Facilitation and Coordination Group \[CTFG\] Recommendations related to contraception and pregnancy testing in clinical trials, Appendix 5), not breastfeeding, and at least one of the following conditions applies:

∙ Not a woman of childbearing potential (WOCBP) as defined by CTFG Recommendations (Appendix 5) or

‣ A WOCBP who agrees to follow the contraceptive guidance per CTFG Recommendations (Appendix 5) during the treatment period and for at least 120 days (corresponding to time needed to eliminate any study treatments) after the last dose of study treatment.