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)

Key Inclusion Criteria:

1. 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

2. 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

3. Part 1 additional criteria:

   1. 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)
   2. 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

4. Part 2 additional criteria:

   1. Newly diagnosed VTE within 5 days (120 hours) of randomization (with imaging confirmation) as described in the protocol
   2. Anticoagulation therapy with a therapeutic dose of a DOAC for at least 6 months is indicated for newly diagnosed VTE

Key Exclusion Criteria:

1. Is at high risk of intracranial bleeding in the opinion of the investigator

2. 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)

3. Contraindication to anticoagulation in the opinion of the investigator

4. Life expectancy of < 6 months

5. Part 1 participants with cancer and Part 2 additional exclusion criteria:

   1. Has acute leukemia or myelodysplastic syndrome
   2. Has primary brain tumor
   3. Has brain metastases as described in the protocol

6. Part 1 additional exclusion criteria:

   1. Has a symptomatic PE
   2. Has an asymptomatic (incidentally-diagnosed) PE in a segmental or larger pulmonary artery

7. Part 2 additional exclusion criteria: PE leading to hemodynamic instability as described in the protocol

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