Niraparib Monotherapy as Maintain and Recurrent Treatment of Endometrial Serous Carcinoma

This study tests niraparib, a targeted drug that blocks a DNA repair protein, as a treatment for serous endometrial cancer (a type of uterine cancer) that is at an advanced stage or has come back after platinum-based chemotherapy. **You may be eligible if:** - You are a woman 18 or older diagnosed with serous endometrial cancer (stage III or IV) or another type of endometrial cancer - You have completed at least 6 cycles of platinum-based chemotherapy and your disease responded (stable or improved) - OR you have relapsed after multiple lines of chemotherapy and have a BRCA mutation or HRD (DNA repair deficiency) - Your blood counts and organ function meet minimum levels - You are willing to use contraception if you could become pregnant **You may NOT be eligible if:** - You have had prior treatment with a PARP inhibitor (like olaparib or rucaparib) - You have uncontrolled brain metastases - You have active HIV, hepatitis B, or hepatitis C - You have a history of myelodysplastic syndrome (MDS) or AML - You have had recent surgery or significant bone marrow radiation - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.