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.