Study of Niraparib With Radiotherapy for Treatment of Metastatic Invasive Carcinoma of the Cervix

Inclusion Criteria: 1. Participant must have histologically confirmed diagnosis of invasive squamous cell or adenocarcinoma of the cervix, FIGO Stage IIIC2 or IV (see Appendix 5 of the currently approved protocol). 2. Participant must have an Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 1. 3. Participant must be ≥ 18 years of age. 4. Participant must have adequate organ function within 28 days of registration, defined as follows: * Absolute neutrophil count ≥ 1,500/µL * Platelets ≥ 100,000/µL * Hemoglobin ≥ 9 g/dL * Serum creatinine ≤ 1.5 x upper limit of normal (ULN) or calculated creatinine clearance ≥ 30 mL/min using the Cockcroft-Gault equation * Total bilirubin ≤ 1.5 x ULN (≤2.0 in patients with known Gilberts syndrome) OR direct bilirubin ≤ 1 x ULN * Aspartate aminotransferase and alanine aminotransferase ≤ 2.5 x ULN unless liver metastases are present, in which case they must be ≤ 5 x ULN 5. Participant receiving corticosteroids may continue as long as their dose is stable for least 4 weeks prior to initiating protocol therapy. 6. Participant must agree to not donate blood during the study or for 90 days after the last dose of study treatment. 7. Female participant of childbearing potential must have a negative serum pregnancy test within 14 days prior to registration. Pregnancy test should be repeated within 7 days before CT simulation if more than 14 days has passed since the previous pregnancy test. (If serum test is falsely positive, pregnancy can be excluded by appropriate pelvic imaging.) Patient must agree to abstain from activities that could result in pregnancy from screening through completion of 7 days of pelvic radiotherapy. Females of non-childbearing potential is defined as follows (by other than medical reasons): * ≥45 years of age and has not had menses for \>1 year * Post-hysterectomy, post-bilateral oophorectomy, post external beam radiation of 6 Gy to the pelvis, or post-tubal ligation. Documented hysterectomy or oophorectomy must be confirmed with medical records of the actual procedure or confirmed by a physical exam or imaging. 8. Participant must agree to not breastfeed during the study and for 180 days after the last dose of study treatment. 9. Participant must be able to understand the study procedures and agree to participate in the study by providing written informed consent 10. Participant must have completed 3-6 cycles of platinum based chemotherapy (acceptable regimens in Appendix 7) with clinical evidence of CR (complete response) or PR (partial response) by RECIST criteria no less than 4 weeks and no greater than 12 weeks prior to initiation of protocol therapy. If bevacizumab used, 6 weeks must elapse between administration of bevacizumab and start of radiation therapy. 11. Participant must be eligible for chemoradiation treatment in the opinion of the treating investigator. 12. Participants who are HIV+ must have CD4 counts \>200/dL and demonstrate documented HAART compliance 13. Chemotherapy-related hematological toxicities must have resolved to Grade 1 or less. 14. Participant must have had a CT (chest/abdomen/pelvis) or PET-CT, within 56 days of registration Exclusion Criteria: 1. Participant must not be simultaneously enrolled in any interventional clinical trial. 2. Participant must not have known documented intra-uterine pregnancy. 3. Participant must not have had major surgery ≤ 3 weeks prior to initiating protocol therapy and participant must have recovered from any surgical effects. 4. Participant must not have received investigational therapy ≤ 4 weeks, or within a time interval less than at least 5 half-lives of the investigational agent, whichever is shorter, prior to initiating protocol therapy. Participant that has received prior treatment with a PARP inhibitor is excluded from this study. 5. Participant last treatment with platinum based chemotherapy was ≥12 weeks from initiation of protocol therapy. 6. Participant must not receive any additional chemotherapy while on study. 7. Participant has had radiation therapy encompassing \>20% of the bone marrow within 2 weeks; or any radiation therapy within 1 week prior to Day 1 of protocol therapy. 8. Participant must not have a known hypersensitivity to niraparib components or excipients. 9. Participant must not have received colony stimulating factors (e.g. granulocyte colony-stimulating factor, granulocyte macrophage colony stimulating factor, or recombinant erythropoietin) within 4 weeks prior to initiating protocol therapy. 10. Participant must not have any known history of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). 11. Participant must not have a serious, uncontrolled medical disorder, nonmalignant systemic disease, or active, uncontrolled infection. Examples include, but are not limited to, uncontrolled ventricular arrhythmia, NYHA Class III/IV heart failure, recent (within 90 days) myocardial infarction, uncontrolled major seizure disorder, or any psychiatric disorder that prohibits obtaining informed consent. Participant must not have had a CVA within 6 months of registration. 12. Participant must not have had diagnosis, detection, or treatment of another type of cancer ≤ 2 years prior to initiating protocol therapy (except basal or squamous cell carcinoma of the skin that has been definitively treated).