Inclusion Criteria:

          1. Histologically or cytologically confirmed diagnosis of pancreatic adenocarcinoma with
             locally advanced or metastatic disease

          2. ≥18 years of age

          3. Expected life expectancy of at least 12 weeks

          4. Patients must be able to understand the study procedures and agree to participate in
             the study by providing written informed consent

          5. Patients must have received treatment with platinum-based (cisplatin, oxaliplatin or
             carboplatin) treatment for locally advanced or metastatic pancreatic cancer and have
             received a minimum of 16 weeks of therapy without evidence of disease progression
             based on the investigator's opinion. This does not have to be the patient's current
             treatment.

               -  This requires at least stable imaging and a stable or decreasing tumor marker as
                  applicable and as determined by the investigator.

               -  If a patient has demonstrated a biochemical and imaging response to platinum
                  therapy and has not progressed within 16 weeks of starting this therapy but had
                  to discontinue platinum prior to 16 weeks for a legitimate medical reason (as
                  determined by the investigator), the patient may still be considered for the
                  trial

               -  Patients may have previously failed non-platinum containing therapy or may never
                  have previously progressed on treatment

               -  Discontinuation of the platinum component of the regimen for chemotherapy-related
                  toxicity is permissible provided the patient has previously received at least 16
                  weeks of platinum-based therapy without evidence of disease progression ≤8 weeks
                  after treatment with the platinum agent

               -  Measurable disease is not a requirement for study entry

          6. Patient agrees to peripheral blood samples during screening and at the end of
             treatment for cytogenetic analysis.

          7. Adequate organ function confirmed ≤7 days prior to the first day of study therapy

        Exclusion Criteria:

          1. Prior treatment with a PARP inhibitor, ipilimumab, nivolumab or other cytotoxic
             T-lymphocyte-associated protein (CTLA-4), PD-1 or PD-L1 inhibitor.

          2. Patients who have demonstrated resistance to platinum agents (e.g. oxaliplatin,
             cisplatin) are not eligible to participate in this study

          3. Clinical evidence of uncontrolled malabsorption and/or any other gastrointestinal
             disorder or defect that would, in the opinion of the investigator, interfere with the
             absorption of niraparib

          4. Acute infection requiring intravenous antibiotics, antiviral or antifungal agents
             during the 14 days prior to first dose of study therapy

          5. Patients will be excluded if they have an active, known or suspected autoimmune
             disease, defined as: patients with a history of inflammatory bowel disease are
             excluded from this study, as are patients with a history of symptomatic autoimmune
             disease (eg rheumatoid arthritis, systemic progressive sclerosis (scleroderma),
             systemic lupus erythematosus, autoimmune vasculitis eg Wegener's Granulomatosis);
             motor neuropathy considered of autoimmune origin (eg Guillain-Barre Syndrome).

             NOTE: Patients are permitted to enroll if they have vitiligo, type I diabetes
             mellitus, residual hypothyroidism due to autoimmune condition only requiring hormone
             replacement, psoriasis not requiring systemic treatment, or conditions not expected to
             recur in the absence of an external trigger.

          6. Has a history of interstitial lung disease or active, non-infectious pneumonitis

          7. Has received a live vaccine within 4 weeks prior to the first dose of trial therapy
             (Note: seasonal influenza vaccines for injection are generally inactivated and are
             allowed; however intranasal influenza vaccines (eg. Flu-Mist) are live attenuated
             vaccines and are not allowed

          8. For fertile patient (female able to become pregnant or male able to father a child),
             refusal to use effective contraception during the period of the trial and for 5 months
             after the last dose of study drug.

          9. Received any systemic treatment for pancreatic cancer ≤14 days prior to first dose of
             therapy. Patients must not have had investigational therapy administered ≤ 4 weeks, or
             within a time interval less than at least 5 half-lives of the investigational agent,
             whichever is longer, prior to the first scheduled day of dosing in this study

         10. Patients will be excluded if they have a condition requiring systemic treatment with
             either corticosteroids (>10mg daily prednisone equivalents) or other immunosuppressive
             medications within 14 days of study drug administration. Inhaled or topical steroids
             and adrenal replacement doses >10mg daily prednisone equivalents are permitted in the
             absence of active autoimmune disease.

         11. Patient has had any known Grade 3 or 4 anemia, neutropenia or thrombocytopenia due to
             prior chemotherapy that persisted > 4 weeks and was related to the most recent
             treatment.

         12. Non-study related minor surgical procedure ≤5 days, or major surgical procedure ≤21
             days, prior to the first dose of therapy; in all cases, patients must be sufficiently
             recovered and stable before treatment administration.

         13. Active drug or alcohol use or dependence that would interfere with study compliance.

         14. Presence of any other condition that may increase the risk associated with study
             participation or may interfere with the interpretation of study results, and, in the
             opinion of the investigator, would make the patient inappropriate for entry into the
             study.

         15. Patient must not have any known history of myelodysplastic syndrome (MDS) or acute
             myeloid leukemia (AML)

         16. Patients must not be simultaneously enrolled in any therapeutic clinical trial

         17. Patients must not have had radiotherapy within 4 weeks of the first dose of study
             treatment

         18. Patients must not have a known hypersensitivity to the components of niraparib or the
             excipients

         19. Patients must not have received a transfusion (platelets or red blood cells) ≤ 4 weeks
             of the first dose of study treatment

         20. Patients must not be undergoing treatment for an active cancer at the time of
             randomization. Exceptions include: local therapies for skin cancers and hormonal
             therapies for breast or prostate cancer.

         21. Patients may not have a history of positive test for human immunodeficiency virus
             (HIV) or known acquired immunodeficiency syndrome (AIDS).

         22. Patients must not have known, symptomatic brain or leptomeningeal metastases