Inclusion Criteria:

        Part 1 and Part 2:

          -  Female participant is at least 18 years of age

          -  Participant has histologically or cytologically proven endometrial cancer with
             recurrent or advanced disease.

          -  Participant must have primary Stage III or Stage IV disease or first recurrent
             endometrial cancer with a low potential for cure by radiation therapy or surgery alone
             or in combination and meet at least one of the following criteria; a) Participant has
             primary Stage IIIA to IIIC1 disease with presence of evaluable or measurable disease
             per RECIST v.1.1 based on Investigator's assessment. Lesions that are equivocal or can
             be representative of post-operative change should be biopsied and confirmed for the
             presence of tumor; b) Participant has primary Stage IIIC1 disease with carcinosarcoma,
             clear cell, serous, or mixed histology (containing >=10 percent carcinosarcoma, clear
             cell, or serous histology) regardless of presence of evaluable or measurable disease
             on imaging; c) Participant has primary Stage IIIC2 or Stage IV disease regardless of
             the presence of evaluable or measurable disease; d) Participant has first recurrent
             disease and is naïve to systemic anticancer therapy; e) Participant has received prior
             neo-adjuvant/adjuvant systemic anticancer therapy and had a recurrence or PD >=6
             months after completing treatment (first recurrence only).

          -  Participant has an Eastern Cooperative Oncology Group (ECOG) performance status of 0
             or 1.

          -  Participant has adequate organ function.

          -  Part 2 only:

          -  Participants must have normal blood pressure (BP) or adequately treated and controlled
             hypertension (systolic BP <=140 millimeter of mercury (mmHg) and diastolic BP <=90
             mmHg).

          -  Participants must be able to take medication orally, by mouth (PO).

        Exclusion Criteria:

          -  Part 1 and Part 2:

          -  Participant has received neo-adjuvant/adjuvant systemic anticancer therapy for primary
             Stage III or IV disease and: a) has not had a recurrence or PD prior to first dose on
             the study OR b) has had a recurrence or PD within 6 months of completing systemic
             anticancer therapy treatment prior to first dose on the study.

          -  Participant has had >1 recurrence of endometrial cancer.

          -  Participant has received prior therapy with an anti-programmed cell death protein 1
             (anti-PD-1), anti-PD-ligand 1 (anti-PD-L1), or anti-PD-ligand 2 (anti-PD-L2) agent.

          -  Participant has received prior anticancer therapy (chemotherapy, targeted therapies,
             hormonal therapy, radiotherapy, or immunotherapy) within 21 days or <5 times the
             half-life of the most recent therapy prior to Study Day 1, whichever is shorter.

          -  Participant has a concomitant malignancy, or participant has a prior non-endometrial
             invasive malignancy who has been disease-free for <3 years or who received any active
             treatment in the last 3 years for that malignancy. Non-melanoma skin cancer is
             allowed.

          -  Participant has known uncontrolled central nervous system metastases, carcinomatosis
             meningitis, or both.

          -  Participant has not recovered (i.e., to Grade <=1 or to Baseline) from cytotoxic
             therapy induced AEs or has received transfusion of blood products (including platelets
             or red blood cells) or administration of colony-stimulating factors (including
             granulocyte colony-stimulating factor [G-CSF], granulocyte macrophage
             colony-stimulating factor [GM-CSF], or recombinant erythropoietin) within 21 days
             prior to the first dose of study drug.

          -  Participant is considered a poor medical risk due to a serious, uncontrolled medical
             disorder, nonmalignant systemic disease, or active infection requiring systemic
             therapy.

          -  Participant has received, or is scheduled to receive, a live vaccine within 30 days
             before first dose of study treatment, during study treatment, and for up to 180 days
             after receiving the last dose of study treatment.

          -  Part 2 only:

          -  Participant has clinically significant cardiovascular disease

          -  Participant has any known history or current diagnosis of myelodysplastic syndrome
             (MDS) or acute myeloid leukemia (AML).

          -  Participant is at increased bleeding risk due to concurrent conditions.

          -  Participant has participated in Part 1 of this study.