Trial of Maintenance With Niraparib- Uterine Serous Carcinoma

Study treatment will be administered orally Q day continuously. Up to three capsules of 100mg strength will be taken at each dose administration. Initiation dose will be defined per current FDA guidelines for Niraparib treatment in ovarian cancer. Dose interruption (no longer than 28 days) will be allowed. Dose reduction will be allowed based on treatment side effects. Dose reductions to 2 capsules daily (200mg) and subsequently to 1 capsule daily (100mg) will be allowed. No further dose reductions will be allowed. The timing of efficacy or safety evaluations should not be affected by dose interruptions or reductions.