In this study, eligible participants will be randomized in a 1:1 ratio to receive one of the two dose levels of I-DXd. Randomization will be stratified by:~Prior receipt or of an anti-programmed death-ligand 1 (PD-[L]1) antibody (yes/no)~The chemotherapy-free interval (CTFI) from completion of the first-line therapy to the date of documented radiological Progressive Disease of <90 days vs. ≥90 days in second-line participants as well as the number of previous lines. Thus, the stratification factor includes three categories: (1) second-line participants with CTFI <90 days, (2) second-line participants with CTFI ≥90 days, and (3) third- and fourth-line participants.
This study intends to define the recommended Phase 2 dose of ifinatamab deruxtecan (I-DXd) based on the efficacy, safety, and pharmacokinetics (PK) results observed in participants with Extensive-stage Small Cell Lung Cancer (ES-SCLC) who received at least 1 prior line of platinum-based chemotherapy and a maximum 3 prior lines of therapy and to investigate I-DXd anti-tumor activity in this population.