A Study to Evaluate Dostarlimab Plus Carboplatin-paclitaxel Versus Placebo Plus Carboplatin-paclitaxel in Participants With Recurrent or Primary Advanced Endometrial Cancer

Inclusion Criteria:

Part 1 and Part 2:

• Female participant is at least 18 years of age.

• Participant has histologically or cytologically proven endometrial cancer withrecurrent or advanced disease.

• Participant must have primary Stage III or Stage IV disease or first recurrentendometrial cancer with a low potential for cure by radiation therapy or surgeryalone or in combination and meet at least one of the following criteria;

1. Participant has primary Stage IIIA to IIIC1 disease with presence of evaluableor measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST)version (v).1.1 based on Investigator's assessment. Lesions that are equivocalor can be representative of post-operative change should be biopsied andconfirmed for the presence of tumor;

2. Participant has primary Stage IIIC1 disease with carcinosarcoma, clear cell,serous, or mixed histology (containing greater than or equal to [>=] 10 percentcarcinosarcoma, clear cell, or serous histology) regardless of presence ofevaluable or measurable disease on imaging;

3. Participant has primary Stage IIIC2 or Stage IV disease regardless of thepresence of evaluable or measurable disease;

4. Participant has first recurrent disease and is naïve to systemic anticancertherapy;

5. Participant has received prior neo-adjuvant/adjuvant systemic anticancertherapy and had a recurrence or progression of disease (PD) >=6 months aftercompleting treatment (first recurrence only).

• Participant has an 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 andcontrolled hypertension (systolic BP lesser than or equal to [<=] 140 millimeter ofmercury [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 forprimary Stage III or IV disease and:

1. has not had a recurrence or PD prior to first dose on the study OR

2. has had a recurrence or PD within 6 months of completing systemic anticancertherapy 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 thehalf-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-endometrialinvasive malignancy who has been disease-free for <3 years or who received anyactive treatment in the last 3 years for that malignancy. Non-melanoma skin canceris allowed.

• Participant has known uncontrolled central nervous system metastases, carcinomatosismeningitis, or both.

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

• Participant has not recovered adequately from AEs or complications from any majorsurgery prior to starting therapy.

• Participant is currently participating and receiving study treatment or hasparticipated in a study of an investigational agent and received study treatment orused an investigational device within 4 weeks of the first dose of treatment.

• Participant is considered a poor medical risk due to a serious, uncontrolled medicaldisorder, nonmalignant systemic disease, or active infection requiring systemictherapy.

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

Part 2 only:

• Participant has received prior therapy with a poly (adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor.

• 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