A Study to Test Obrixtamig in Combination With Pumitamig in People With Advanced Small Cell Lung Cancer (Dareon®-Rosetta35)

Inclusion criteria:

1. Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to any trial-specific procedures, sampling, or analyses.
2. Male or female participants ≥18 years old and at least at the legal age of consent in countries where it is greater than 18 years at the time of signature of the Informed Consent Form (ICF).
3. Willing and able to comply with scheduled visits, treatment schedule, the planned trial assessments, laboratory tests, restrictions regarding prohibited medications, lifestyle restrictions, and other requirements related to the trial. This includes that they are able to understand and follow trial-related instructions.
4. Histologically or cytologically confirmed Extensive Stage Small Cell Lung Carcinoma (ES-SCLC) \[using the AJCC (American Joint Committee on Cancer) tumour node metastasis staging system combined with Veterans Administration Lung Study Group (VALG)'s two stage classification scheme\].
5. Prior systemic anti-cancer treatment for ES-SCLC:

   * For Cohort 1 - must have received at least one line of platinum-containing treatment but no more than 2 lines of treatment per local standard of care for the treatment of ES-SCLC.
   * For Cohort 2 - must have received no prior systemic therapy for ES-SCLC. Participants with prior chemoradiotherapy for limited stage (LS)-SCLC must have been treated with curative intent and had a treatment-free interval of at least 6 months after the last chemotherapy, radiotherapy, or chemoradiotherapy before diagnosis of ES-SCLC to be eligible.
6. At least one measurable lesion outside of the Central Nervous System (CNS) as defined per Response Evaluation Criteria In Solid Tumors (RECIST) 1.1. Previously treated lesions after local therapy (radiotherapy, ablation, interventional procedures, etc.) are generally not considered target lesions. If the lesion with prior local treatment is the only measurable lesion, radiologic evidence must be provided to demonstrate disease progression for selection as target lesion (an isolated blastic bone metastasis or a singular central nervous system metastasis should not be considered as a measurable lesion).
7. Availability of an archival tumour sample (except China).
8. Adequate organ function. Further inclusion criteria apply.

Exclusion criteria:

1. Serious concomitant disease or medical condition such as neurologic, psychiatric (including substance use disorder), active ulcers (gastrointestinal tract or skin) or laboratory abnormalities that may negatively impact patient safety during trial participation, affect compliance with trial requirements or invalidate assessments relevant for the investigation of the safety and preliminary efficacy of the investigational drugs.
2. Histologically or cytologically confirmed SCLC with combined histology, diagnosis of Merkel cell carcinoma, medullary thyroid carcinoma or neuroendocrine prostate cancer.
3. Presence of leptomeningeal disease and/or carcinomatous meningitis.
4. Known hypersensitivity to the trial drugs or their excipients, prior severe, life-threatening hypersensitivity reaction(s) to monoclonal antibodies, or significant risk of allergic or anaphylactic reaction(s) to any of the investigated drug products according to the investigator's judgement.
5. Participants who experienced severe, life-threatening immune-mediated adverse events, e.g. serious Grade 3 or higher immune-mediated adverse event (imAE) or infusion-related reactions, that led to permanent discontinuation while on treatment with immuno-oncology agents.
6. Persistent toxicity from previous treatments that has not resolved to ≤ Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 (except for alopecia, asthenia/fatigue, amenorrhea/menstrual disorders, CTCAE Grade 2 peripheral neuropathy, and CTCAE Grade 2 endocrinopathies controlled by replacement therapy, and toxicities, which are considered irreversible but stable for at least 4 weeks, per investigator judgment).
7. Prior organ or tissue allograft.
8. History of or active interstitial lung disease, pulmonary fibrosis, organizing pneumonia or non-infectious pneumonitis (any grade) or any other condition resulting in significant impairment in lung function.

Further exclusion criteria apply.