DAREON™-9: A Study to Test How Well Different Doses of BI 764532 Are Tolerated by People With Small Cell Lung Cancer When Taken Together With a Single Agent Chemotherapy

This study is open to adults with extensive stage small cell lung cancer. The study is in people with advanced cancer that had previously received platinum-based chemotherapy and are eligible to receive a single agent chemotherapy treatment. The purpose of this study is to find the highest dose of BI 764532 that people can tolerate when taken together with a single agent chemotherapy. BI 764532 is an antibody-like molecule that may help the immune system fight cancer. Participants may continue to take BI 764532 as long as they benefit from treatment and can tolerate it. During this time, participants visit the study site regularly. The visits also depend on the response to the treatment. At the study visits, the doctors check the health of the participants, take necessary laboratory tests, and note any health problems that could have been caused by the study treatment.

Inclusion Criteria: 1. 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). 2. Signed and dated written informed consent in accordance with International Conference of Harmonization-Good Clinical Practice (ICH-GCP) and local legislation prior to admission to the trial. 3. Histologically or cytologically confirmed small cell lung cancer (SCLC). Patients with tumours with mixed histology are eligible only if SCLC component is predominant and represent at least 50% of the overall tumour tissue. 4. Extensive stage - small cell lung cancer (ES-SCLC) that progressed or recurred following platinum-based treatment, and anti- programmed cell death protein 1 (PD-1) or programmed cell death ligand 1 (PD-L1) as applicable. 5. Patients must be eligible for single agent chemotherapy treatment (used in the trial) according to label. 6. Availability of archival tumour tissue sample. 7. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1. Further inclusion criteria apply. Exclusion Criteria: 1. Previous treatment in this trial. 2. Current enrolment in another investigational device or drug trial, or \