Atezolizumab in this study is expected to have a positive benefit-risk profile for the treatment of patients with platinum-sensitive relapse of ovarian cancer. Of interest, atezolizumab is being investigated also in combination with platinum-based doublet chemotherapy in second line (2L)/ third line (3L) platinum-sensitive recurrent ovarian cancer patients in ATALANTE (NCT02891824), which also includes bevacizumab in the combination. The study is proceeding as expected after >100 patients enrolled and under independent Data Monitoring Committee (IDMC) supervision.

Platinum-containing therapy is considered the treatment of choice for patients with platinum-sensitive relapse. However the duration of response and the prolongation of the progression free interval with chemotherapy are usually brief, among other because these chemotherapy regimens cannot be continued until progression as they are associated with neurological, renal and hematological toxicity and cannot generally be tolerated for more than about 6 to 9 cycles.

Niraparib received FDA approval in March 2017 as maintenance treatment of adult patients with recurrent epithelial ovarian, fallopian tube or primary peritoneal cancer who are in complete or partial response to platinum-based chemotherapy. Recently, the European Medicines Agency (EMA) has also approved niraparib as maintenance monotherapy. Despite the progress brought about by niraparib, there is a need for a more effective treatment to extend the progression free interval in this patient population. The combination with immune checkpoint inhibitors such as anti-death protein 1 (anti-PD1) or anti-death protein ligand 1 (anti-PD-L1) has a compelling rationale to this aim, especially under the light of the emerging clinical data of this combination.

The use of atezolizumab concurrent to platinum-containing chemotherapy followed by niraparib as maintenance therapy after completion of chemotherapy, as per normal clinical practice, may provide further benefit to patients in terms of prolonging the progression free interval and increasing the interval between lines of chemotherapy, hence delaying further hospitalization and the cumulative toxicities associated with chemotherapy. Additionally, preliminary studies with atezolizumab suggest an acceptable tolerability profile for long term clinical use in recurrent ovarian cancer patients and other indications.

Inclusion Criteria:

1. Patients ≥ 18 years old

2. Life expectancy ≥3 months

3. Signed informed consent and ability to comply with treatment and follow-up

4. Histologically confirmed diagnosis (cytology alone excluded) of high- grade serous or endometrioid ovarian, primary peritoneal or tubal carcinoma.

5. Breast Cancer (BRCA) mutational status is known (germline or somatic)

6. Relapsed disease more than 6 months after the last platinum dose

7. No more than 2 prior lines of chemotherapy are allowed, and the last one must contain a platinum-based regimen

8. At least one measurable lesion to assess response by RECIST v1.1 criteria.

9. Mandatory de novo tumor biopsy (collected within 3 months prior to randomization) sent to HistoGene X as a formalin-fixed, paraffin-embedded (FFPE) sample for PD-L1 status determination for randomization. The inclusion of patients with non informative tissue PD-L1 status will be capped to 10% of the whole study population:

   • If the mandatory de novo biopsy is technically not possible or failed to produce enough representative tumor tissue, an FFPE sample from archival tissue may be acceptable after approval of the sponsor.
   • Bone metastases, fine needle aspiration, brushing, cCell pellet from pleural effusion, or ascites or lavage are not acceptable.

10. Two additional tumour samples are needed: Archival tumor sample must be available for exploratory PD-L1 testing in archival tissue and archival or "de novo" tissue sample for biomarkers must also be available.

11. Performance status determined by Eastern Cooperative Oncology Group (ECOG) score of 0-1

12. Normal organ and bone marrow function:

    • Haemoglobin ≥10.0 g/dL
    • Absolute neutrophil count (ANC) ≥1.5 x 109/L
    • Lymphocyte count ≥0.5 × 109/L
    • Platelet count ≥100 x 109/L
    • Total bilirubin ≤1.5 x institutional upper limit of normal (ULN)
    • Serum albumin ≥2.5 g/dL
    • Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) ≤2.5 x ULN, unless liver metastases are present in which case they must be ≤5 x ULN
    • Serum creatinine ≤1.5 x institutional ULN or calculated creatinine clearance ≥ 30 mL/min using the Cockcroft-Gault equation
    • Patients not receiving anticoagulant medication must have an International Normalized Ratio (INR) ≤1.5 and an Activated ProThrombin Time (aPTT) ≤1.5 x ULN.

13. Negative Test Results for Hepatitis.

14. Toxicities related to previous treatments must be recovered to < grade 2

15. Female participants must be postmenopausal or surgically sterile or otherwise have a negative serum pregnancy test within 7 days of the first study treatment and agree to abstain from heterosexual intercourse or use single or combined contraceptive methods.

16. Participant must agree to not donate blood during the study or for 90 days after the last dose of study treatment.

17. Participant must agree to not breastfeed during the study or for 180 days after the last dose of study treatment.

Exclusion Criteria:

1. Non-epithelial tumor of the ovary, the fallopian tube or the peritoneum.
2. Ovarian tumors of low malignant potential or low grade
3. Other malignancy within the last 5 years except curatively treated non-melanoma skin cancer, in situ cancer of the cervix and ductal carcinoma in situ (DCIS)
4. Major surgery within 4 weeks of starting study treatment or patients who have not completely recovered (Grade ≥ 2) from the effects of any major surgery at randomization
5. Core biopsy or other minor surgical procedure, excluding placement of a vascular access device, within 7 days prior to Day 1, Cycle 1
6. Administration of other chemotherapy drugs, anticancer therapy or anti-neoplastic hormonal therapy, or treatment with other investigational agents or devices within 28 days prior to randomization, or within a time interval less than at least 5 half-lives of the investigational agent, whichever is shorter, or anticipation to do it during the trial treatment period (non-investigational hormonal replacement therapy is permitted)
7. Palliative radiotherapy (e.g., for pain or bleeding) within 6 weeks prior to randomization or patients who have not completely recovered (Grade ≥ 2) from the effects of previous radiotherapy
8. Current or recent (within 10 days prior to randomization) chronic use of aspirin (>325 mg/day) or clopidogrel (>75 mg/day)
9. Clinically significant (e.g. active) cardiovascular disease
10. Resting ECG with corrected QT interval (QTc) >470 msec on 2 or more time points within a 24 hour period or family history of long QT syndrome
11. Left ventricular ejection fraction defined by multigated acquisition/echocardiogram (MUGA/ECHO) below the institutional lower limit of normal
12. History or clinical suspicion of brain metastases or spinal cord compression. CT/MRI of the brain is mandatory (within 4 weeks prior to randomization) in case of suspected brain metastases. Spinal MRI is mandatory (within 4 weeks prior to randomization) in case of suspected spinal cord compression
13. History or evidence upon neurological examination of central nervous system (CNS) disorders (e.g. uncontrolled epileptic seizures) unless adequately treated with standard medical therapy
14. Current, clinically relevant bowel obstruction, including sub-occlusive disease, related to underlying disease
15. Uncontrolled tumor-related pain
16. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures (once monthly or more frequently). Patients with indwelling catheters (e.g., PleurX) are allowed
17. Uncontrolled hypercalcemia (>1.5 mmol/L ionized calcium or calcium >12 mg/dL or corrected serum calcium > ULN) or symptomatic hypercalcemia requiring continued use of bisphosphonate therapy or denosumab
18. Evidence of any other disease, metabolic dysfunction, physical examination finding or laboratory finding giving reasonable suspicion of a disease or condition that contraindicates the use of an investigational drug or puts the patient at high risk for treatment related complications
19. Pregnant or lactating women
20. Simultaneously receiving therapy in any interventional clinical trial
21. Prior treatment with CD137 agonists or immune checkpoint stimulating or blockade therapies, such as anti-PD1, anti-PDL1 or anti-CTLA4 therapeutic antibodies
22. Treatment with systemic immunostimulatory agents (including but not limited to interferon-alpha (IFN-α) and interleukin-2 (IL-2) within 4 weeks or five half-lives of the drug (whichever is shorter) prior to Cycle 1, Day 1
23. Treatment with systemic corticosteroids or other systemic immunosuppressive medications (including but not limited to prednisone, dexamethasone, cyclophosphamide, azathioprine, methotrexate, thalidomide, and anti-tumor necrosis factor (TNF) agents) within 2 weeks prior to Cycle 1, Day 1, or anticipated requirement for systemic immunosuppressive medications during the trial
24. History of autoimmune disease, including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, vascular thrombosis associated with anti-phospholipid syndrome, Wegener's granulomatosis, Sjögren's syndrome, Guillain-Barré syndrome, multiple sclerosis, vasculitis, or glomerulonephritis
25. History of idiopathic pulmonary fibrosis (including pneumonitis), drug-induced pneumonitis, organizing pneumonia (i.e., bronchiolitis obliterans, cryptogenic organizing pneumonia), or evidence of active pneumonitis
26. Immunocompromised patients, e.g., patients who are known to be serologically positive for human immunodeficiency virus (HIV)
27. Signs or symptoms of infection within 2 weeks prior to Cycle 1, Day 1
28. Active tuberculosis
29. Administration of a live, attenuated vaccine (including against influenza) within 4 weeks prior to Cycle 1, Day 1 or anticipation that it will be administered at any time during the treatment period of the study or within 5 months after the final dose of atezolizumab.
30. History of severe allergic, anaphylactic, or other hypersensitivity reactions to chimeric or humanized antibodies or fusion proteins
31. Known hypersensitivity or allergy to biopharmaceuticals produced in Chinese hamster ovary cells or to any component of the atezolizumab formulation or allergy to any of the other drugs included in the protocol or their solvents (including to Cremophor®)
32. Patient has received prior treatment with a poly (adenosine diphosphate (ADP)-ribose) polymerase (PARP) inhibitor in the recurrent setting or has participated in a study where any treatment arm included administration of a PARP inhibitor in the recurrent setting, unless the patient is unblinded and there is evidence of not having received a PARP inhibitor. Patients that received PARP inhibitor as front line are eligible for the study. The duration of exposure to PARPi following front line therapy needs to be ≥18 months for BRCA mutated patients and ≥ 12 months for BRCA wild type patients.
33. Patient has had any known ≥Grade 3 hematological toxicity anemia, neutropenia or thrombocytopenia due to prior cancer chemotherapy that persisted >4 weeks and was related to the most recent treatment
34. Patient has any known history or current diagnosis of Myelodysplasic syndrome (MDS) or Anaplastic Myeloid Leukemia (AML)
35. Previous allogeneic bone marrow transplant or previous solid organ transplantation
36. Patient has a condition (such as transfusion dependent anemia or thrombocytopenia), 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
37. Participant has any known hypersensitivity to niraparib components or excipients

Atezolizumab and placebo treatment will be double blinded, unknown to both the subject and the study staff, including the treating physician. In order to maintain the blind, atezolizumab and placebo will be identical in appearance and packaging.

The study medication will be labeled using a unique kit id number, which is linked to the randomization scheme. The active and placebo kits will be presented in the same packaging to ensure blinding of the study medication Individual treatment codes, indicating the treatment randomization for each randomized patient, will be available to the investigator(s) or pharmacists from the IVRS/IWRS. Routines for this will be described in the Interactive Voice Response System/Interactive Web Response System (IVRS/IWRS) user manual that will be provided to each centre.