A Study Comparing Niraparib Versus Platinum-Taxane Doublet Chemotherapy as Neoadjuvant Treatment in Participants With Homologous Recombination-Deficient Stage III/IV Ovarian Cancer (COHORT-C)

Inclusion Criteria:

* Participant has newly diagnosed Stage III or IV ovarian, fallopian tube, or primary peritoneal cancer according to the International Federation of Gynecology and Obstetrics staging criteria.
* Participants must provide sufficient tumor tissue at Prescreening and agree to undergo a central HRD tumor testing using a fully validated assay. The participants must be HRd as per central HRD tumor testing result for eligibility.

  1. Participants with a documented germline breast cancer susceptibility gene (BRCA) 1/2 deleterious or suspected deleterious mutations by Sponsor's permitted test (e.g., BRACAnalysis CDx) may be allowed to enroll prior to receiving the central test results, provided all inclusion criteria are met. However, tumor sample submitted by these participants will still be required for central HRD confirmation. The list of Sponsor's permitted tests will be provided by the Sponsor.
  2. All participants must agree to provide tumor tissue collected from IDS.
  3. Participant must provide 2 formalin-fixed paraffin-embedded tissue blocks (or slides if blocks are not available) with sufficient tumor content (as confirmed by the Sponsor's designated central and/or testing laboratory) for central HRD testing at Prescreening and for exploratory biomarker testing at Prescreening or Screening. If sufficient tumor tissue is provided at Prescreening, participants do not need to provide additional tissue at Screening.
* Participant must have completed 1 run-in cycle of carboplatin-paclitaxel and not experienced disease progression after this treatment. Completion is defined as receiving ≥50% of the prescribed dose of therapy within 5 weeks.
* Participant must not have known contraindication or uncontrolled hypersensitivity to carboplatin and paclitaxel and their excipients and no known pre-existing conditions that would preclude treatment with these agents.
* Participant must not have known contraindication or uncontrolled hypersensitivity to niraparib and its excipients.
* Participant must not have symptomatic ascites or pleural effusions as defined by the following criterion: presence of fluid in the abdominal or pleural cavities requiring removal within 1 week prior to signing the informed consent.
* Participant must agree to complete Patient-reported outcome (PRO) and work productivity questionnaires throughout the study.

Exclusion Criteria:

* Participant has low-grade or Grade 1 epithelial Ovarian Cancer (OC) or mucinous, germ cell, transitional cell, carcinosarcoma, or undifferentiated tumor.
* Participant has contraindications to surgery.
* Participant has a bowel obstruction by clinical symptoms or Computed tomography (CT) scan, subocclusive mesenteric disease, abdominal or gastrointestinal fistula, gastrointestinal perforation, or intra-abdominal abscess.
* 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 (e.g., major injuries or major surgery within the past 28 days prior to the start of study treatment and/or history of hemorrhagic stroke, transient ischemic attack, subarachnoid hemorrhage, or clinically significant hemorrhage within the past 3 months).
* Participant is immunocompromised. Participants with splenectomy are allowed. Participants with known Human immunodeficiency virus (HIV) are allowed if they meet all of the following criteria:

  1. Cluster of differentiation 4-positive T cell count ≥350/μL and viral load \<400 copies/mL
  2. No history of Acquired immunodeficiency syndrome (AIDS)-defining opportunistic infections within 12 months prior to enrollment
  3. No history of HIV-associated malignancy for the past 5 years
  4. Concurrent antiretroviral therapy as per the most current National Institutes of Health Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents Living with HIV started \>4 weeks prior to study enrollment
* Participant received prior treatment for high-grade non-mucinous epithelial ovarian, fallopian tube, or peritoneal cancer (e.g., prior surgery, immunotherapy, anticancer therapy \[with the exception of 1 run-in cycle of carboplatin-paclitaxel\], or radiation therapy).
* Participant has an active autoimmune disease that has required systemic treatment in the past 2 years. Replacement therapy is not considered a form of systemic therapy (e.g., thyroid hormone or insulin).
* Participant is unable to swallow orally administered medication or has a gastrointestinal disorder likely to interfere with absorption of the study medication.
* Participant received whole blood transfusions in the 2 weeks prior to entry to the study (packed red blood cells and platelet transfusions are acceptable outside of 2 weeks prior to treatment).