Inclusion Criteria:

          1. Signed written informed consent

          2. Men aged 18 years or older

          3. ECOG performance status: 0-1,

          4. Histologically confirmed extracranial primary germ cell cancer, seminoma, or
             nonseminoma

          5. Rising serum markers (i.e., alpha-fetoprotein and human chorionic gonadotropin) on
             sequential measurement or biopsy-proven unresectable germ cell cancer

          6. Refractory GCTs e.g. patients relapsing after high-dose chemotherapy or for patients
             non fit enough for high-dose chemotherapy

          7. Primary mediastinal GCTs in first relapse

          8. Patient's disease must not be amenable to cure with either surgery or chemotherapy in
             the opinion of investigator,

          9. Measurable disease radiologically

         10. Adequate hematologic function defined by ANC > 1500/mm3, platelet count > 100 000/mm3
             and hemoglobin level > 9g/dl.

         11. Adequate liver function defined by a total bilirubin level < 1.5 ULN, and ALT, AST < 3
             ULN or < 5 in case of liver metastases. For subjects with Gilbert's syndrome bilirubin
             > 1.5 × ULN is allowed if no symptoms of compromised liver function are present

         12. Adequate renal function: measured or calculated (by Cockcroft formula) creatinine
             clearance > 50 ml/min. Cockcroft formula: CLcr = [(140-age) x weight(Kg)]/[72 x
             creatinine (mg/dl)]

         13. At least 4 weeks must have elapsed since the last radiotherapy and/or chemotherapy
             before study entry,

         14. At least 4 weeks must have elapsed since the last major surgery

         15. Complete recovery from prior surgery, and/or reduction of all adverse events from
             previous systemic therapy or radiotherapy to grade 1,

         16. Absence of any psychological, familial, sociological or geographical condition
             potentially hampering compliance with the study protocol and follow-up schedule

        Exclusion Criteria:

          1. Patients who do not fit inclusion criteria

          2. Other prior malignancy except successfully treated nonmelanoma skin cancer

          3. Prior PARP1 inhibitor

          4. Other concurrent approved or investigational anticancer treatment, including surgery,
             radiotherapy, chemotherapy, biologic-response modifiers, hormone therapy, or
             immunotherapy

          5. Female patients

          6. Patients infected by the Human Immunodeficiency Virus (HIV)

          7. Patients with other severe acute or chronic medical condition, or laboratory
             abnormality that would impair, in the judgment of investigator, excess risk associated
             with study treatment, or which, in judgment of the investigator, would make the
             patient inappropriate for entry into this study

          8. Inability of oral intake, or drug absorption (e.g. malabsorption syndrome)

          9. Hypersensitivity to any compound of the drug

         10. Sexually active men not using highly effective birth control if their partners are
             women of child-bearing potential

         11. Patients with history of or current CNS metastasis

         12. Patients with history of seizures