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)

Key Inclusion Criteria:

1. Has a histologically confirmed diagnosis of malignant solid tumors which are locally advanced or metastatic as described in the protocol
2. Has a Khorana thromboembolic risk score ≥2 during screening period or harbors a somatic documented tumor genetic variant known to be associated with a similar increased risk of VTE as described in the protocol
3. Has an Eastern Cooperative Oncology Group (ECOG) Performance Status 0 to 2 at the time of screening and day 1 prior to the first dose of study intervention

Key Exclusion Criteria:

1. Has 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)
2. Has a cancer diagnosis consisting solely of basal cell or squamous cell skin carcinoma
3. Has a primary brain tumor or brain metastases as described in the protocol
4. Has proximal lower extremity DVT locally detected by Compression Ultrasound (CUS) during screening period
5. Has any condition that, as judged by the investigator, may confound the results of the study or would place the participant at increased risk of harm if he/she participated in the study

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