This study is researching an experimental drug called REGN7508 (called "study drug"). The study is focused on the prevention of Cancer-Associated Thrombosis (CAT) in participants. The aim of the study is to see how effective the study drug is in preventing blood clots in participants with solid tumors who are currently receiving anticancer treatment or planning to start anticancer treatment within a month of being assigned to a study treatment, or recovering from surgery, and how the study drug compares to placebo for CAT. The study is looking at several other research questions, including: * What side effects may happen from taking the study drug * How much study drug is in the blood at different times * Whether the body makes antibodies against the study drug (which could make the study drug less effective or could lead to side effects)