A Phase 1/2 Study of REGN4018 (A MUC16×CD3 Bispecific Antibody) Administered Alone or in Combination with Cemiplimab in Patients with Recurrent Ovarian Cancer or Other Recurrent MUC16+ Cancers

The main purpose of this study is to:

- Learn about the safety of ubamatamab and to find out what dose of ubamatamab can be
given alone or with cemiplimab to patients with ovarian cancer or cancer of the
uterus

- The study will also look at the levels of ubamatamab and/or cemiplimab in the body
and measure how well the body can remove the study drug(s). This is called
pharmacokinetics

- The study will also look at any signs that ubamatamab alone or with cemiplimab can
treat recurrent advanced ovarian cancer or cancer of the uterus

- To find out how safe and tolerable pretreatment is in combination with ubamatamab
and to see how well it works to prevent or minimize Cytokine Release Syndrome (CRS)

Key Inclusion Criteria:

1. Ovarian Cancer Cohorts Only: Patients with histologically or cytologically confirmed
diagnosis of advanced, epithelial ovarian cancer (except carcinosarcoma), primary
peritoneal, or fallopian tube cancer who have all of the following:

1. serum CA-125 level ≥2 x upper limit of normal (ULN) (in screening, not required
for low-grade serous carcinoma)

2. has received at least 1 line of platinum-containing therapy or must be
platinum-intolerant (applicable for dose escalation and non-randomized dose
expansion cohorts)

3. documented relapse or progression on or after the most recent line of therapy

4. no standard therapy options likely to convey clinical benefit

2. Adequate organ and bone marrow function as defined in the protocol

3. Life expectancy of at least 3 months

4. Randomized phase 2 expansion cohort (Ovarian Cancer only): Platinum-resistant
ovarian cancer patients who have had 2 to 4 lines of platinum-based therapy as
defined in the protocol.

5. Endometrial Cancer Cohorts Only: histologically confirmed endometrial cancer that
has progressed or recurrent after prior anti-Programmed Cell Death Ligand 1 (PD-1)
therapy and platinum-based chemotherapy:

1. MUC16 positivity of tumor cells ≥25% by immunohistochemistry (IHC), as defined
in the protocol

2. 1-4 prior lines of systemic therapy, as described in the protocol

Key Exclusion Criteria:

1. Prior treatment with anti-Programmed Cell Death (PD-1)/PD-L1 therapy, as described
in the protocol

2. Ovarian Cancer Expansion cohorts only: More than 4 prior lines of cytotoxic
chemotherapy (does not apply to low-grade serous ovarian cancer cohort)

3. Prior treatment with a MUC16 - targeted therapy

4. Untreated or active primary brain tumor, central nervous system (CNS) metastases, or
spinal cord compression, as described in the protocol

5. History and/or current cardiovascular disease, as defined in the protocol

6. Severe and/or uncontrolled hypertension at screening. Patients taking
anti-hypertensive medication must be on a stable anti-hypertensive regimen

Note: Other protocol-defined Inclusion/Exclusion Criteria apply