A Study to Test How BI 764532 is Taken up by Tumours in People With Small-cell Lung Cancer or Neuroendocrine Cancer

Inclusion Criteria: * Age ≥18 years * Weight ≥ 60kg * Signed and dated, written informed consent form (ICF) in accordance with International Council for Harmonisation-Good Clinical Practice (ICH-GCP) and local legislation prior to any trial-specific procedures, sampling, or analyses. * Patient who failed conventional treatment or for whom no therapy of proven efficacy exists or who is not eligible for established treatment options. Patient must have exhausted available treatment options known to prolong survival for their disease. Previous therapies should include at least one line of platinum-based chemotherapy. Previous therapy with anti Programmed Cell Death Protein 1 (PD-1) or Programmed Cell Death Ligand 1 (PD-L1) are allowed. * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1. * At least one evaluable lesion outside of Central Nervous System (CNS) as defined per Response Evaluation Criteria in Solid Tumours (RECIST) 1.1 * Subjects with brain metastases are eligible provided they meet the following criteria: * radiotherapy or surgery for brain metastases was completed at least 2 weeks 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 CNS disease. Further inclusion criteria apply. Exclusion Criteria: * Previous or concomitant malignancies other than the one treated in this trial within the last 2 years except: * effectively treated non-melanoma skin cancers * effectively treated carcinoma in situ of the cervix * effectively treated ductal carcinoma in situ * other effectively treated malignancy that is considered cured by local treatment * Major injuries and/or surgery or bone fracture within 28 days of first dose BI 764532, or planned surgical procedures * Known leptomeningeal disease or spinal cord compression due to metastatic disease * Anticoagulant treatment that cannot be safely interrupted based on opinion of the investigator if medically needed * Active infection that requires medical therapy or other clinically significant intervention * Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection within 2 weeks prior to study entry (confirmed via polymerase chain reaction (PCR) test or other applicable test as per local requirements) or suspected SARS-CoV-2 infection as per physician assessment, or close contact (within 1 week) with an individual with confirmed SARS-CoV-2 infection * Any of the following known laboratory evidence of hepatitis virus infection: * Positive results of hepatitis B surface (HBs) antigen * Presence of hepatitis B core (HBc) antibody together with hepatitis B virus DNA (HBV-DNA) * Presence of hepatitis C ribonucleic acid (RNA) * Known human immunodeficiency virus (HIV) infection. Further exclusion criteria apply.