DAREON™-7: A Study to Test How Well Different Doses of BI 764532 in Addition to Chemotherapy Are Tolerated by People With Advanced Neuroendocrine Cancers

Inclusion Criteria: * 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) * Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to any trial-specific procedures, sampling, or analyses * Patients diagnosed with locally advanced or metastatic NEC of following subtypes: * extrapulmonary neuroendocrine carcinomas (epNEC) * pulmonary large cell NEC (LCNEC) * neuroendocrine carcinomas (NEC) of unknown primary site * Patients with tumours with mixed histologies for any above type are eligible only if neuroendocrine carcinoma/small tumour cells component is predominant and represent at least 50% of the overall tumour tissue * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 * Minimum life expectancy of 12 weeks * At least one measurable lesion as defined per RECIST 1.1 within approximately 35 days prior to the first dose of BI 764532 * Patients with a history of asymptomatic Central nervous system (CNS) metastases are eligible, provided they meet all of the following criteria: * No radiotherapy (including whole brain radiation therapy, stereotactic radiotherapy or radiosurgery) within 7 days * Are neurologically stable without the need for steroids or anti-convulsants for at least 7 days before first dose of BI 764532 as per local site assessment Further inclusion criteria apply. Exclusion Criteria: * Previous treatment in this trial * Current enrolment in another investigational device or drug trial, or \<30 days since ending another investigational device or drug trial(s) * Patients with diagnosis of Merkel cell carcinoma or medullary thyroid carcinoma or Grade 3 neuroendocrine tumour * Presence of leptomeningeal carcinomatosis * Previous treatment with DLL3-targeting T cell engagers and cell therapies * Patients who have been treated with extensive field radiotherapy including whole brain irradiation within 2 weeks prior to first administration of BI 764532 * 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 Any documented active or suspected malignancy or history of malignancy within 5 years prior to Screening (other than the target indication or well differentiated neuroendocrine tumour (NET) stages of the target indication in case of transformed tumors), except for appropriately treated basal cell carcinoma of the skin or in situ carcinoma of uterine cervix Further exclusion criteria apply.