A Study to Evaluate Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Preliminary Anti-tumor Activity of RO7616789 in Advanced Small Cell Lung Cancer and Other Neuroendocrine Carcinomas

Inclusion Criteria:

* Life expectancy at least 12 weeks
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
* Adequate hematologic and end organ function
* Negative serum pregnancy test.
* Adequate contraception and no or interruption of breastfeeding
* Histologically confirmed extensive SCLC or poorly differentiated NEC of any other origin, relapsed after at least 1 systemic therapy
* Measurable disease according to Response Evaluation criteria in Solid Tumors (RECIST) Version 1.1
* Confirmed availability of representative archival tumor specimens in formalin-fixed, paraffin-embedded (FFPE) blocks or unstained slides

Exclusion Criteria:

* Pregnant or breastfeeding, or intending to become pregnant during the study or within 40 days after the final dose of study treatment
* Poorly controlled Type 2 diabetes mellitus defined as a screening hemoglobin A1c ≥ 8% or a fasting plasma glucose ≥ 160 mg/dL (or 8.8 mmol/L)
* QT interval corrected using Fridericia's formula (QTcF) \> 470 ms. Abnormal electrocardiograms (ECGs) (triplicate) should be performed \> 30 minutes apart
* Current treatment with medications that are well known to prolong the QT interval
* Prior treatment with anti-cluster of differentiation (CD)137 agents, anti-CD3 agents and/or delta-like ligand 3 (DLL3) targeted therapies
* Any anti-cancer therapy, whether investigational or approved, including chemotherapy, hormonal therapy, or radiotherapy, within 21 days prior to initiation of study treatment
* Any history of an immune-related Grade 4 adverse event (AE) attributed to prior anti-programmed death ligand-1 (PD-L1) /PD-1 or anti-cytotoxic T-lymphocyte-associated protein (CTLA-4) therapy (other than asymptomatic elevation of serum amylase or lipase)
* Any history of an immune-related Grade 3 adverse event attributed to prior anti-PD-L1 /PD-1 or anti-CTLA-4 therapy (other than asymptomatic elevation of serum amylase or lipase) that resulted in permanent discontinuation of the prior immunotherapeutic agent
* History or clinical evidence of primary central nervous system (CNS) malignancy, symptomatic CNS metastases, CNS metastases requiring any anti-tumor treatment, or leptomeningeal disease and current or history of CNS disease, such as stroke, epilepsy, CNS vasculitis, or neurodegenerative disease
* Spinal cord compression that has not been definitively treated with surgery and/or radiation
* Active or history of clinically significant autoimmune disease
* Positive test for human immunodeficiency virus (HIV) infection
* Positive hepatitis B surface antigen (HbsAg) test, and/or positive total hepatitis B core antibody (HbcAb) test at screening
* Prior allogeneic hematopoietic stem cell transplantation or prior solid organ transplantation
* Administration of a live, attenuated vaccine within 4 weeks before first RO7616789 infusion
* Known allergy or hypersensitivity to any component of the RO7616789 formulation