• Phase I, open-label interventional biodistribution trial

The trial will be carried out in two consecutive steps:

• Step 1: The aim of the first step is to assess the whole-body tissue and tumour
  penetration/distribution of [89Zr]Zr-BI 764532 at baseline and potential needs for mass dose
  optimization (i.e. need for additional mass dose).
• Step 2: In the second step the aim is to determine the blocking pattern of BI 764532 treatment by
  applying different treatment doses prior to on-treatment PET scans.

• The primary endpoint of this trial is the mean relative change from baseline (Cycle 1 Day 1)
  of [89Zr]Zr-BI 764532 tumour-to-plasma ratios in all detectable lesions post BI 764532 doses.

• Age ≥18 years
• Weight ≥ 60kg
• Signed and dated, written informed consent form (main ICF.
• Diagnosed with locally advanced, metastatic or relapsed cancer not amenable to curative treatment of the following histologies:
  a. Small cell lung carcinoma (SCLC)
  b. Large cells neuroendocrine lung carcinoma (LCNEC)
  c. Neuroendocrine carcinoma (NEC) or small cell carcinoma of any other origin
• 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 PD-1 or PD-L1 are allowed.
• Performance status of 0-1 (ECOG)
• At least one evaluable lesion outside of CNS
• Subjects with brain metastases are eligible provided they meet the following criteria:
  o radiotherapy or surgery for brain metastases was completed at least 2 weeks prior to the first administration of BI 764532,
  o patient is off steroids for at least 7 days (physiologic doses of steroids are permitted
  o patient is off anti-epileptic drugs for at least 7 days or on stable doses of anti-epileptic drugs for malignant CNS disease.
• Adequate organ function
• Male or female patients. Women of childbearing potential (WOCBP) and men able to father a child must be ready and able to use highly effective methods of birth control

• Previous treatment with T cell Engager (TcE) or cell therapies targeting DLL3. Other DLL3 targeting agents (like Rovalpituzumab tesirine (RovaT)) are allowed only if DLL3 positivity is documented after completion of treatment with DLL3 targeting agent in post-treatment biopsy.
• Anticoagulant treatment that cannot be safely interrupted based on opinion of the investigator if medically needed (e.g. biopsy).
• Persistent toxicity from previous treatments that has not resolved to = Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 (except for alopecia, CTCAE Grade 2 neuropathy, asthenia/fatigue or grade 2 endocrinopathies controlled by replacement therapy).
• Patient has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of BI 764532. Physiological replacement of steroids is allowed.
• Prior anti-cancer therapy:
  o Patients who have been treated with any other anti-cancer drug within 3 weeks or within 5 half-life periods (whichever is shorter) prior to first administration of BI 764532.
  o Patients who have been treated with extensive field radiotherapy including whole brain irradiation within 2 weeks prior to first administration of BI 764532.
• Other active malignancy that could interfere with the prognosis and treatment of the disease of the study.
• Major surgery within 28 days of first dose BI 764532.
• Women who are pregnant (including those who are considered to be possibly pregnant based on the investigator's clinical judgement), nursing/breast feeding or who plan to become pregnant or nurse while in the trial or within 35 days after the last dose of study treatment.
• Active infection that requires medical therapy or other clinically significant intervention or within 2 weeks prior to study entry confirmed (PCR test or other applicable test as per local requirements) or suspected SARS-CoV-2 infection or close contact with an individual with confirmed SARS-CoV-2 infection.