PRIMARY OBJECTIVES:~I. To evaluate whether niraparib tosylate monohydrate (niraparib) shows preliminary evidence of clinical activity among subjects with leiomyosarcoma (LMS) with genomic alterations in the homologous recombination (HR) pathway as measured by the confirmed objective response rate (ORR).~SECONDARY OBJECTIVES:~I. To evaluate the clinical benefit rate (CBR) associated with niraparib treatment in the study population.~II. To evaluate the progression free survival (PFS) associated with niraparib treatment in the study population.~III. To evaluate the overall survival (OS) associated with niraparib treatment in the study population.~IV. To evaluate the overall safety and tolerability of niraparib treatment in the study population.~EXPLORATORY OBJECTIVES:~I. To evaluate predictive biomarkers of response to niraparib. II. To evaluate genomic mechanisms of resistance following treatment benefit with niraparib.~III. To evaluate previous treatment response as a marker of response to niraparib.~OUTLINE:~Patients receive niraparib orally (PO) once daily (QD). Cycles repeat every 28 days for 15 months in the absence of disease progression or unacceptable toxicity.~After completion of study treatment, patients are followed up for 5 years or until death.
This phase II trial tests whether niraparib works to shrink tumor in patients with leiomyosarcoma. Niraparib is an inhibitor of PARP, an enzyme that helps repair deoxyribonucleic acid (DNA) when it becomes damaged. Blocking PARP may help keep cancer cells from repairing their damaged DNA, causing them to die. PARP inhibitors are a type of targeted therapy.