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)

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 topotecan treatment 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 <30 days since
ending another investigational device or drug trial(s)

3. Untreated or symptomatic brain metastases. Participants with treated, stable brain
metastases are eligible provided they meet the following criteria:

- Radiotherapy or major surgery for brain metastases was completed at least 2 weeks
(for radiotherapy) or 4 weeks (for major brain metastases surgery) prior to the
first administration of BI 764532.

- Patient is off steroids for at least 7 days (physiologic doses of steroids are
permitted), and the patient is off anti-epileptic drugs for at least 7 days or on
stable doses of anti-epileptic drugs for malignant central nervous system (CNS)
disease.

4. Presence of leptomeningeal carcinomatosis

5. Previous treatment with T cell engager (TcE) or cell therapies targeting delta-like
ligand 3 (DLL3).

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, CTCAE Grade 2 neuropathy, or Grade 2 endocrinopathies controlled by
replacement therapy).

7. Major surgery (major according to the investigator's assessment) within 28 days prior
to first administration of BI 764532 or planned during treatment period, e.g. hip
replacement.

8. Previous or concomitant malignancies other than the one treated in this trial within
the last 2 years except

1. effectively treated non-melanoma skin cancers

2. effectively treated carcinoma in situ of the cervix

3. effectively treated ductal carcinoma in situ

4. other effectively treated malignancy that is considered cured by local treatment
Further exclusion criteria apply

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Eligibility last updated 8/28/23. Questions regarding updates should be directed to the study team contact.