Study of Tarlatamab in Combination With YL201 With or Without Anti-programmed Death Ligand 1 (PD-L1) in Participants With Extensive Stage (ES) Small Cell Lung Cancer (SCLC)

Who May Qualify: - Participants ≥ 18 years of age (or legal adult age within country) at time of signing willing to sign a consent form. - Participants with diagnosed by tissue sample (biopsy-confirmed) ES-SCLC. - For Parts 1 and 2, participant must have ES-SCLC that has progressed or recurred following at least 1 line of platinum-based anti-cancer therapy. - For Part 3, participants must have ES-SCLC and no prior systemic treatment for ES SCLC other than 1 cycle of platinum-based chemotherapy, etoposide, and PD-(L)1 inhibitor in the first-line setting. - At least 1 measurable lesion as defined by RECIST 1.1. - Participants must have your organs (liver, kidneys, etc.) are working well enough based on blood tests (cardiac, pulmonary, kidney, bone marrow, and liver). Who Should NOT Join This Trial: - Prior delta-like ligand 3 (DLL3) or B7 homolog 3 (B7-H3) targeted therapy. - Prior exposure to topoisomerase I inhibitors or antibody-drug conjugate (ADC) with topoisomerase I inhibitor payload. - Symptomatic central nervous system (CNS) metastases. Note: Participants with asymptomatic brain metastases are eligible as defined in the protocol. - History of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required corticosteroids, current ILD/pneumonitis, or suspected ILD/pneumonitis that cannot be ruled out by imaging at screening. - Baseline requirement of supplemental oxygen. Always talk to your doctor about whether this trial is right for you.