• Signed informed consent prior to any study specific procedures;

• Female, age ≥ 18 years at time of signing informed consent

• Patients with high-grade serous or endometroid ovarian, fallopian tube, or primary peritoneal cancer recurrent or progressive after first line PARPi maintenance are allowed;

• Patients must have received only one previous line of a platinum containing regimen not containing bevacizumab;

• Patient must have received a first-line maintenance therapy with a PARPi for at least 6 months, if the prior PARPi used was olaparib then patients must have received treatment without significant toxicity or the need for a permanent dose reduction.Patients who experience disease relapse after the end of the 24 months maintenance therapy are eligible;

• Patients must have undergone secondary cytoreductive surgery. The cytoreduction must result in complete resection (absence of macroscopic residual tumor) or at least resection of the progressive lesion(s) occurring during maintenance;

• Documented BRCA1/2 status. Both mutated and wild type patients are eligible. Patient with unknown status of BRCA genes agrees to undergo analysis of their germline and somatic BRCA status (testing must be completed prior to enrolment in the study);

• Patients must have a life expectancy ≥ 16 weeks;

• Patients must start the experimental treatments in the current study within 3 to 8 weeks from second surgery;

• ECOG performance status 0 to 1;

• Patient must provide archival tumor samples formalin fixed, paraffin embedded (FFPE) from both the primary and secondary surgeries for paired analysis. A quality control analysis of samples will be performed before patient's randomization;

• Patient must be able to take oral medications;

• Patients must have normal organ and bone marrow function measured within 28 days prior to administration of study treatment as defined below:

‣ Haemoglobin ≥ 10.0 g/dL with no blood transfusion in the past 28 days

⁃ Absolute neutrophil count (ANC) ≥ 1.5 x 109/L

⁃ Platelet count ≥ 100 x 109/L

⁃ Total serum bilirubin ≤ 1.5 x institutional upper limit of normal (ULN)

⁃ Aspartate aminotransferase (AST) (Serum Glutamic Oxaloacetic Transaminase (SGOT)) and Alanine aminotransferase (ALT) (Serum Glutamic Pyruvate Transaminase (SGPT)) ≤ 2.5 x ULN for the institution (or ≤ 5x ULN if liver metastases are present)

⁃ Patients must have creatinine clearance estimated of ≥51 mL/min using the Cockcroft-Gault equation or based on a 24 hour urine test: Estimated creatinine clearance = (140-age \[years\]) x weight (kg) (x F)a serum creatinine (mg/dL) x 72 (a where F=0.85 for females.

• Postmenopausal or evidence of non-childbearing status for women of childbearing potential: negative urine or serum pregnancy test within 28 days of study treatment and confirmed prior to treatment on Day 1 Cycle 1. Postmenopausal is defined as:

‣ Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) levels in the post-menopausal range for women under 50;

⁃ radiation-induced oophorectomy with last menses \>1 year ago;

⁃ chemotherapy-induced menopause with \>1-year interval since last menses;

⁃ surgical sterilisation (bilateral oophorectomy or hysterectomy).

• Women of childbearing potential and their partners, who are sexually active, must agree to the use of one highly effective forms of contraception and their partners must use a male condom, during the treatment and for at least 1 months after last dose of olaparib.For chemotherapy drugs, please refer to fertility section of corresponding Summary of Product Characteristics (SCP);

• Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests, and other trial procedures;