This study is researching an experimental drug called ubamatamab, also referred to as "study drug". The study is focused on patients who have advanced ovarian cancer.

The aim of the study is to see how safe, tolerable, and effective the study drug is on its own and in combination with other anti-cancer drugs (bevacizumab, cemiplimab, fianlimab and a standard chemotherapy drug, pegylated liposomal doxorubicin [PLD]), referred to as "combination drugs'.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drug and its experimental combinations
• How much study drug and fianlimab 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) and its combinations

Key Inclusion Criteria:

1. Participants with histologically or cytologically confirmed diagnosis of advanced serous or endometrioid ovarian (regardless of the grade), primary peritoneal, or fallopian tube cancer (clear cell, mucinous, and carcinosarcoma are excluded)
2. Must have progression on prior therapy documented radiographically and must have at least 1 measurable lesion (not previously irradiated) that can be accurately measured by RECIST 1.1
3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
4. Adequate organ and bone marrow function, as described in the protocol
5. Platinum-Resistant Ovarian Cancer, as described in the protocol

Key Exclusion Criteria:

1. Major surgical procedure or significant traumatic injury within 4 weeks prior to first dose of study intervention(s)
2. Documented allergic or acute hypersensitivity reaction attributed to antibody treatments or doxorubicin hydrochloride or components of study intervention(s)
3. Another malignancy that is progressing or requires active treatment, as described in the protocol
4. Untreated or active Central Nervous System (CNS) metastases, or carcinomatous meningitis, as described in the protocol
5. Uncontrolled infections including but not limited to human immunodeficiency virus, hepatitis B or hepatitis C infection, or diagnosis of immunodeficiency
6. Moderate to large or ascites, as described in the protocol
7. Bowel obstruction within last 3 months or current need for parenteral nutrition

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