BL-M14D1 Plus Atezolizumab vs Standard of Care in First-Line Extensive-Stage Small Cell Lung Cancer (BrenDeLL-Lung01)

Inclusion Criteria: * Histologically or cytologically confirmed first-line (1L), extensive-stage (ES) small cell lung cancer (SCLC) * Must be eligible to receive a platinum-based chemotherapy regimen in combination with an anti-PD-L1 inhibitor. * At least one measurable lesion based on RECIST v1.1 per investigator assessment. * An Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1. * Adequate organ function Exclusion Criteria: * Received any kind of platinum or etoposide treatment for limited stage (LS) SCLC within 6 months prior to enrollment. * Participants who have received prior topoisomerase inhibitor-based ADC therapy. * Participants with history of severe heart disease * Participants with active autoimmune diseases and inflammatory diseases, * Participants with other prior or concurrent malignancies except for basal cell carcinoma of the skin, squamous cell carcinoma of the skin and/or carcinoma in situ after adequate resection, or other malignancy treated with curative intent with a disease-free interval of at least 3 years * Other protocol-defined inclusion/exclusion criteria apply.