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)

Inclusion Criteria:

• Participants ≥ 18 years of age (or legal adult age within country) at time ofsigning informed consent.

• Participants with histologically or cytologically confirmed ES-SCLC.

• For Parts 1 and 2, participant must have ES-SCLC that has progressed or recurredfollowing at least 1 line of platinum-based anti-cancer therapy.

• For Part 3, participants must have ES-SCLC and no prior systemic treatment for ESSCLC other than 1 cycle of platinum-based chemotherapy, etoposide, and PD-(L)1inhibitor in the first-line setting.

• At least 1 measurable lesion as defined by RECIST 1.1.

• Participants must have adequate organ function (cardiac, pulmonary, kidney, bonemarrow, and liver).

Exclusion Criteria:

• 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) withtopoisomerase I inhibitor payload.

• Symptomatic central nervous system (CNS) metastases. Note: Participants withasymptomatic brain metastases are eligible as defined in the protocol.

• History of (non-infectious) interstitial lung disease (ILD)/pneumonitis thatrequired corticosteroids, current ILD/pneumonitis, or suspected ILD/pneumonitis thatcannot be ruled out by imaging at screening.

• Baseline requirement of supplemental oxygen.