This study is researching an experimental drug called 89Zr-DFO-REGN5054 and cemiplimab. The study is focused on patients with a type of cancer that can be potentially imaged using 89Zr-DFO-REGN5054 and show special tumor features that may be important to the way the immune system fights cancer.

The aim of the study is to study the safety and tolerability (how the body reacts to the drug) of the imaging agent 89Zr-DFO REGN5054.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drugs
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drugs (which could make the study drugs less effective or could lead to side effects)

Key Inclusion Criteria:

• Advanced or metastatic solid tumors that may respond to anti-programmed cell death 1 (PD-1) immunotherapy
• Measurable disease according to Response Evaluation Criteria in Solid Tumours (RECIST) 1.1 criteria
• Eastern Cooperative Oncology Group (ECOG) performance status of ≤1
• Adequate organ and bone marrow function as defined in the protocol
• Willing and able to comply with clinic visits and study-related procedures (including required tumor biopsy for Part B)

Key Exclusion Criteria:

• Currently receiving another cancer treatment or inadequate time since last therapy, as defined in the protocol
• Has not yet recovered from acute toxicities from prior therapy; exceptions defined in the protocol
• Prior treatment with a blocker of the PD-1/Programmed death ligand 1 (PD-L1) pathway
• Currently receiving or has received chimeric antigen receptor (CAR-T) cell therapy
• Symptomatic or untreated brain metastases, leptomeningeal disease, or spinal cord compression
• Known history of or any evidence of interstitial lung disease, active, noninfectious pneumonitis (past 5 years) or active tuberculosis

NOTE: Other protocol defined inclusion/exclusion criteria apply.

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf