An Open-Label, Multicenter, Long-term Treatment Extension Study in Subjects Who Have Completed a Prior GlaxoSmithKline/TESARO-Sponsored Niraparib Study and Are Judged by the Investigator to Benefit From Continued Treatment With Niraparib

Inclusion Criteria: * Participant is able to understand the study procedures and agrees to participate in the study by providing written informed consent. * Participant is willing and able to comply with scheduled visits, treatment plans, and any other study procedures. * Participant is currently receiving treatment with niraparib (as monotherapy or in combination) in a GlaxoSmithKline/TESARO-sponsored study that has fulfilled the requirements for the primary objective. * Participant is currently benefiting from treatment with niraparib as assessed by the Investigator according to the parent study protocol requirements. * Participants of childbearing potential who are sexually active and their partners must agree to the use of an effective form of contraception throughout their participation during study treatment through 180 days after last dose of study drug. Exclusion Criteria: * Participant has been permanently discontinued from niraparib treatment in the parent study for any reason. * Participant currently has unresolved toxicities for which niraparib dosing has been interrupted in the parent study. Participants meeting all other eligibility criteria may be enrolled once toxicities have resolved to allow niraparib treatment to resume. * Participant is pregnant or is expecting to conceive children while receiving study drug or for up to 180 days after the last dose of study drug. Participant is breastfeeding or is expecting to breastfeed within 30 days of receiving the final dose of study drug (women should not breastfeed or store breastmilk for use during niraparib treatment and for 30 days after receiving the final dose of study treatment).