Niraparib Maintenance Treatment in Patients With Newly Diagnosed Advanced Platinum- Sensitive, OC. The First Poland RWE Study.

Inclusion Criteria: 1. Patients must be female, ≥18 years of age, able to understand the study procedures, and agree to participate in the study by providing written informed consent. 2. Patients with a histologically confirmed diagnosis of nonmucinous high - grade epithelial ovarian cancer (serous, endometrial) that is stage III or IV according to the FIGO criteria. 3. All patients with Stage IV disease are eligible. This includes those with inoperable disease, those who undergo PDS (R0 or macroscopic disease), or those for whom NACT is planned. 4. Patients with Stage III are eligible if they meet the following criteria: 1. All FIGO III patients in spite of residual disease and cytoreductive surgery. 2. All patients with inoperable Stage III disease. 3. All Stage III patients after NACT chemotherapy. 5. FFPE tumor tissue sample must be available for molecular analysis. 6. Patients of childbearing potential must have a negative serum or urine pregnancy test (beta human chorionic gonadotropin) within 72 hours prior to receiving the first dose of study treatment. 7. Patients must be postmenopausal, free from menses for \>1 year, surgically sterilized, or willing to use highly effective contraception to prevent pregnancy (see 0) or must agree to abstain from activities that could result in pregnancy throughout the study, starting with enrollment through 180 days after the last dose of study treatment. 1. Serum creatinine ≤1.5 × upper limit of normal (ULN) or calculated creatinine clearance ≥60 mL/min using the Cockcroft-Gault equation 2. Total bilirubin ≤1.5 × ULN or direct bilirubin ≤1.5 × ULN 3. AST and ALT ≤2.5 × ULN unless liver metastases are present, in which case they must be ≤5 × ULN 8. Patients must have an ECOG score of 0 or 1. 9. Patients must have normal BP or adequately treated and controlled hypertension. 10. Patients must be able to take oral medication. Exclusion Criteria: 1. Patient has mucinous, germ cell, transitional cell, or undifferentiated tumor. 2. Patient has low-grade or Grade 1 epithelial ovarian cancer. 3. Patient has a known condition, therapy, or laboratory abnormality that might confound the study results or interfere with the patient's participation for the full duration of the study treatment in the opinion of the Investigator. 4. Patient is pregnant or is expecting to conceive children while receiving study drug or for up to 180 days after the last dose of study drug. Patient is breastfeeding or is expecting to breastfeed within 30 days of receiving the final dose of study drug (women should not breastfeed or store breastmilk for use, during niraparib treatment and for 30 days after receiving the final dose of study treatment). 5. Patient has any known history or current diagnosis of MDS or AML. 6. Hypersensitivity to the active substance or to any of the excipients including tartrazine. 7. Hypertension-Participants have systolic BP \>140 mmHg or diastolic BP \>90 mmHg that has not been adequately treated or controlled. 8. Patients with prior history of PRES.