Multicentre, 2 arm, open-label UK randomised phase II trial to determine the efficacy of niraparib versus active symptom control (ASC) in patients who have relapsed after previously receiving platinum based systemic therapy. 84 patients will be recruited from approximately 10 UK trial network sites.

Mesothelioma is a cancer that is caused by exposure to asbestos, an environmental contaminant. This cancer is incurable and lacks effective treatment, particularly after initial chemotherapy. There has not been a licenced therapy for mesothelioma since 2003, and no treatment has yet demonstrated an improvement in survival following initial chemotherapy. There is an urgent need to explore more effective approaches to therapy. Targeted treatments offer potential hope for the treatment of mesothelioma. A class of drugs called PARP (Poly Adenosine Diphosphate-ribose polymerase) inhibitors have already been proven to improve the survival of patients with breast and ovarian cancers, that carry specific mutations. Mesothelioma has been shown in a recent trial to respond to this class of agent. Further investigation is warranted to test whether PARP inhibitors could be a new treatment option for patients. As with ovarian cancer studies of the past, the NERO trial will test a PARP inhibitor (niraparib) after successful treatment with chemotherapy. Patients whose tumours shrink or stabilise following chemotherapy are expected to have a greater chance of benefit from niraparib. It's not known if niraparib will be able to improve survival of patients with mesothelioma, or indeed whether or not toxicity could occur without benefit. For that reason, patients will be randomised with a 2:1 chance of receiving the drug. Those patients who do not receive niraparib will be closely monitored for signs of early tumour growth so that they can go on to receive an alternative treatment if necessary. If the NERO trial is positive, this study will lead to the approval of a new medicine for use around the world, one that would extend the life expectancy of patients for the first time following initial chemotherapy. NERO will recruit 84 patients over 12 months. Those randomised to receive niraparib will receive a daily dose of 200 mg or 300mg for up to 24 weeks within the trial.

Inclusion Criteria:

• Patients must have signed and dated a REC-approved written informed consent form in accordance with regulatory and institutional guidelines. This must be obtained before the performance of any protocol-related procedures that are not part of normal patient care.

• Patients must be willing and able to comply with scheduled visits, treatment schedule, laboratory tests, and other requirements of the study

• Histologically confirmed diagnosis of mesothelioma. Any histological subtype (epithelioid, biphasic or sarcomatoid) and any site (e.g. pleural or peritoneal) with an available tissue block. Tissue blocks will be requested at the time of screening.

• Patients must have received prior systemic therapy (any number of lines) for pleural or peritoneal mesothelioma.

• Disease progression must be confirmed per Investigator's assessment prior to screening.

• Any prior treatment must be completed at least 14 days prior to receiving study treatment, where all toxicities have recovered or returned to grade 1, with the exception of alopecia and neuropathy due to chemotherapy which should have returned to grade 2.

• Eastern Cooperative Oncology Group Performance Status (ECOG PS) 0-1.

• Radiologically assessable disease by modified RECIST (pleural mesothelioma) or RECIST 1.1 (non-pleural mesothelioma or where measurements for modified RECIST cannot be obtained).

• Age ≥ 18 years old.

• Consent to provide mandatory diagnostic tissue blocks and blood samples for translational research, including an optional rebiopsy at progression.

• Adequate organ function, including suitable bone marrow reserve and creatinine clearance.

• Screening laboratory values must meet the following criteria within 48 hours prior to commencement of treatment:

  1. White blood cells ≥ 2 x 109/L
  2. Neutrophils ≥ 1.5 x 109/L
  3. Platelets ≥ 100 x 109/L
  4. Haemoglobin ≥ 90 g/L
  5. Serum creatinine of ≤ 1.5 X ULN or creatinine clearance (CrCl) > 50 mL/minute (using Cockcroft/Gault formula)
  6. AST ≤ 3 x ULN OR ALT ≤ 3 x ULN (if both are assessed, both need to be ≤ 3 x ULN)
  7. Total bilirubin ≤ 1.5 x ULN (except patients with Gilbert Syndrome, who must have total bilirubin < 51.3 μmol/L)

• Reproductive status:

  1. Women of childbearing potential (WOCBP) must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of Human Chorionic Gonadotropin) at enrolment and within 24 hours prior to the start of study treatment. An extension up to 3 days prior to the start of study treatment may be permissible in situations where results cannot be obtained within a 24-hour window.
  2. Women must not be breastfeeding
  3. WOCBP must agree to use a highly effective method of contraception for the duration of treatment and 180 days after the last dose ASC+Niraparib.
  4. Men who are sexually active with WOCBP must use the contraceptive methods outlines in the protocol for the duration of treatment and for 90 days after the last dose of ASC+Niraparib

• Expected survival of at least 12 weeks per Investigator's assessment

Exclusion Criteria:

• Patients with untreated, symptomatic central nervous system (CNS) metastases, including carcinomatous meningitis, leptomeningeal disease, and radiographic signs of CNS haemorrhage are excluded.
• Patients with untreated third space fluid collection requiring therapeutic drainage are excluded
• Second malignancy within 5 years except cancers definitely treated curative intent (e.g. basal cell carcinoma of the skin, squamous cell carcinoma of the skin, in situ bladder cancer or in situ cervical cancer).
• Any serious or uncontrolled medical disorder or active infection that, in the opinion of the investigator, may increase the risk associated with study participation, study drug administration, or would impair the ability of the patient to receive protocol therapy.
• Difficulty swallowing or previous significant resection of the stomach or small bowel.
• Patients who have not recovered from the effects of major surgery or significant traumatic injury at least 14 days before the first dose of study treatment.
• Prior exposure to PARP inhibitor or known hypersensitivity to the components of niraparib.
• New York Heart Associated class II or greater heart failure, hepatic [AST > 3XULN, ALT > 3XUL, Total bilirubin > 1.5XULN] or renal impairment [Serum creatinine of >1.5 X ULN or creatinine clearance (CrCL) ≤ 50 mL/minute (using Cockcroft/Gault formula)].
• Known alcohol or drug abuse.
• Patients are not permitted to enter any other interventional studies.
• Any patient not able to give consent.
• Any pregnant or breastfeeding patient.
• Patient with known history or current diagnosis of myelodysplastic syndrome (MDS) or acute myeloid leukaemia (AML)
• Patient with known history of active tuberculosis.
• Patients with uncontrolled hypertension.
• Participants have current active pneumonitis within 90 days of planned start of the study or a known history of interstitial lung disease, drug-related pneumonitis, or radiation pneumonitis requiring steroid treatment.
• Patients that have received colony-stimulating factors (eg, granulocyte macrophage colony-stimulating factor or recombinant erythropoietin) within 2 weeks prior to the first dose of study treatment.
• Live vaccines within 30 days prior to the first dose of study treatment and while participating in this clinical study.
• Known history of testing positive for human immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome (AIDS).
• Any positive test for hepatitis B virus or hepatitis C virus indicating acute or chronic infection.

IPD will be made available, including data dictionaries, for approved data sharing requests. Individual participant data will be shared that underlie the results after de-identification and normalisation of information (text, tables, figures, and appendices). The study protocol and statistical analysis plan will also be available. Pseudonymised participant data within the clinical trial dataset will be available for sharing via controlled access by authorised Southampton Clinical Trials Unit (SCTU) staff. The request for data access will need to detail the specific requirements and the proposed research, statistical analysis, publication plan and evidence of research group qualifications. Data will be shared once all parties have signed relevant data sharing documentation covering SCTU conditions for sharing and if required, an additional data sharing agreement from the sponsor. Proposals should be directed to ctu@soton.ac.uk.

Anonymous data will be available for request from 3 months after the publication of the results to researchers who provide a completed data sharing request form that describes a methodologically sound proposal, for the purpose of the approved proposal and if appropriate, signed a data-sharing agreement.

Data access requests will be reviewed against specific eligibility criteria by the SCTU data custodian and key members of the trial team.