This study will make it possible to evaluate the efficacy and safety of use of the combination of two products: niraparib and Dostarlimab (also called TSR-042). It will assess whether these two drugs can not only stop the growth of tumor cells but also activate immune cells to kill them.~Patients that tolerates these products well will also be monitored~The investigating doctor suggests that paient take part in this study because his disease may benefit from the treatments administered in this study. Only patients whose tumor is likely to respond to the drugs administered, based on preclinical results or clinical data, will be able to participate in this study. Patient are selected because his tumor seems to have the characteristics that allow him to be included in one of the following three cohorts:~Cohort 1: tumor has a particular mutation; this cohort will include 5 groups according to the type of cancer: bladder cancer (group 1A), cancer of the stomach or of the esophago-gastric junction (group 1B), head and neck cancer (group 1C), bile duct cancer (group 1D) or other cancers (group 1E) Cohort 2: tumor is bladder cancer and has shrunk under previous treatment with platinum salts Cohort 3: clear cell kidney cancer. These products have already been tested in combination and their combination has shown that it is possible without causing toxicity.~About 120 patients will participate in the study in several centers in France. All patients will receive the combination of these two treatments.
Treatment will consist of a PARP inhibitor (niraparib) monotherapy priming period (cycle 0; 21 days); an anti-PD-1 antibody (Dostarlimab ; TSR-042) will then be added from C1D1 every 21 days in combination for the first 4 cycles, and then every 42 days. Disease will be assessed every 2 cycles (6 weeks) from C3D1 by CT-scan (or MRI or bone scan, if relevant). Patients still under treatment after 1 year may have tumor evaluation spaced out every 3 cycles