A Study of ImmunoPet Imaging Using 89Zr-DFO-REGN5054 in Adult Participants With Solid Cancers Treated With Cemiplimab

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)