A Study to Evaluate the Effectiveness and Tolerability of a Second Maintenance Treatment in Participants With Ovarian Cancer, Who Have Previously Received Polyadenosine 5'Diphosphoribose [Poly (ADP Ribose)] Polymerase Inhibitor (PARPi) Treatment.

Participants who have had drainage of their ascites during the final 2 cycles of their last chemotherapy regimen or during the period between completion of chemotherapy and first dose of study treatment.

Participants with current signs or symptoms of bowel obstruction, including sub-occlusive disease, related to underlying disease.

History of leptomeningeal carcinomatosis.

Participants with symptomatic uncontrolled brain metastases.

1. A scan to confirm the absence of brain metastases is not required.

2. Participants whose brain metastases have been treated may participate provided they show radiographic stability. In addition, any neurologic symptoms that developed either as a result of the brain metastases or their treatment must have resolved or be stable (Common Terminology Criteria for Adverse Events \[CTCAE\] Grade \<2) either, without the use of steroids, or are stable on a steroid dose of ≤10 mg/day of prednisone or its equivalent and stable on anti convulsants if required for at least 14 days prior to the start of treatment.

History of another primary malignancy except for:

1. Malignancy treated with curative intent and with no known active disease ≥5 years before the first dose of IP and of low potential risk for recurrence;

2. Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease;

3. Adequately treated carcinoma in situ without evidence of disease.

Major surgical procedures (as defined by the investigator) ≤28 days of beginning study treatment, or minor surgical procedures ≤7 days. No waiting period required following port a cath or other central venous access placement.

Participants with myelodysplastic syndrome (MDS) /acute myeloid leukemia (AML) or with features suggestive of MDS/AML.

Resting electrocardiogram indicating uncontrolled, potentially reversible cardiac conditions, as judged by the investigator, or participants with congenital long QT syndrome.

Known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients.

History of allogeneic organ transplantation including previous allogeneic bone marrow transplant or double umbilical cord blood transplantation.

History of active primary immunodeficiency.

Active infection including tuberculosis (TB), hepatitis B (known positive hepatitis B virus \[HBV\] surface antigen \[HBsAg\] result), hepatitis C (HCV), or human immunodeficiency virus (HIV) (positive HIV 1/2 antibodies). Participants with a past or resolved HBV infection are eligible. Participants positive for HCV antibody are eligible only if polymerase chain reaction is negative for HCV ribonucleic acid.

Uncontrolled intercurrent illness, including but not limited to, ongoing or active infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable angina pectoris, uncontrolled cardiac arrhythmia, active interstitial lung disease, serious chronic gastrointestinal conditions associated with diarrhea, or psychiatric illness/social situations.

Current dependency on total parenteral nutrition or intravenous (iv) fluid hydration.

Whole blood transfusions in the last 120 days prior to entry to the study.

Cytotoxic chemotherapy, hormonal or non hormonal targeted therapy within 21 days of Cycle 1, Day 1 is not permitted. The participant can receive a stable dose of bisphosphonates or denosumab for bone metastases, before and during the study as long as these were started at least 5 days prior to study treatment.

Participation in another clinical study with an IP during the chemotherapy course immediately prior to randomisation or during the course of the study.

Previous treatment with ceralasertib or other ataxia telangiectasia and Rad3-related protein, Checkpoint kinase 1 or deoxyribonucleic acid damage response inhibitor (excluding PARPi).

Exposure to a small molecule IP within 30 days or 5 half-lives (whichever is longer) prior to randomization. The minimum washout period for immunotherapy and bevacizumab shall be 42 days.

Receipt of live attenuated vaccine within 30 days prior to the first dose of study treatment.

Concomitant use of known strong cytochrome P450 (CYP) 3A inhibitors or moderate CYP3A inhibitors. The required washout period prior to starting study treatment is 2 weeks.

Concomitant use of known strong CYP3A inducers or moderate CYP3A inducers. The required washout period prior to starting study treatment is 5 weeks for enzalutamide or phenobarbital and 3 weeks for other agents.

Involvement in the planning and/or conduct of the study (applies to Sponsor staff and/or staff at the study site).

Previous randomization in the present study.

Judgment by the investigator that the participant should not participate in the study if the participant is unlikely to comply with study procedures, restrictions and requirements.

Pregnant or lactating women.

What this study is about