Combination Niraparib and Dostarlimab Therapy for Recurrent or Persistent Uterine Serous Carcinoma

Inclusion Criteria: * Participant must have recurrent or persistent uterine serous carcinoma based on previous biopsy or surgery, and have previously received at least carboplatin/paclitaxel. Mixed and carcinosarcoma histology cases will be eligible if there is a serous component in the tumor * Participant must have an Eastern Cooperative Oncology Group (ECOG) performance status of =\< 1 * Participant must be \>= 18 years of age * Patient has archival tumor tissue available or a fresh biopsy of recurrent or persistent tumor must be obtained prior to study treatment initiation * Patient must have measurable disease by RECIST * No more than three prior chemotherapy regimens (does not include chemoradiation) are permitted. One of the previous lines of treatment must include carboplatin and paclitaxel * Prior PD1/PDL1 inhibitors (including single-agent pembrolizumab, other immunotherapy agents, or combination pembrolizumab and lenvatinib) therapy will be allowed if the patient did not have immune associated toxicity leading to discontinuation. * Patients who have progressed on prior PD1/PDL1 inhibitors may be allowed to participate if the study PI and treating physician deem it to be within the patient's best interest. * Prior chemoradiation therapy for adjuvant treatment or pelvic recurrence is permitted. Chemotherapy in this setting, is not counted as prior line of chemotherapy * Absolute neutrophil count \>= 1,500/uL * Platelets \>= 100,000/uL * Hemoglobin \>= 9 g/dL * Ser…