This study is researching an experimental drug called REGN7508 (called "study drug") and will consist of 2 parts: Part 1 and Part 2. The study is focused on participants with or without cancer who develop blood clots in certain veins (called Deep Vein Thrombosis \[DVT\]) that block blood flow (Part 1) or focused on participants with cancer who develop blood clots in certain veins (DVT) or the lungs (also called Pulmonary Embolism \[PE\]) (Part 2).
The aim of the study is to see how safe and effective the study drug is at treating and preventing further blood clots in participants with or without cancer (Part 1) or in participants with cancer (Part 2) compared with another treatment (apixaban).
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 drug less effective or could lead to side effects)
Has an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 2 at the time of screening and day 1 prior to first dose of study intervention
In Part 1 participants with cancer and Part 2 participants: Histologically confirmed diagnosis of malignant solid or select hematologic tumor (other than basal-cell or squamous-cell carcinoma of the skin alone) as described in the protocol
Has newly diagnosed symptomatic lower extremity DVT or incidentally-detected proximal lower extremity DVT (eg, popliteal or femoral) within 5 days (120 hours) of randomization (with imaging confirmation)
Anticoagulation therapy with a therapeutic dose of a Direct Oral Anticoagulant (DOAC) for at least 3 months is indicated for the newly diagnosed proximal lower extremity DVT
Is at high risk of intracranial bleeding in the opinion of the investigator
Known bleeding conditions (eg, Hemophilia A or B, von Willebrand's disease), hemorrhagic tumor sites, or other conditions with a high risk for bleeding (eg, hepatic disease associated with coagulopathy)
Contraindication to anticoagulation in the opinion of the investigator
Life expectancy of < 6 months