An Open-label, Single Arm, Phase II Trial of Niraparib in Combination With Anti-PD1（Programmed Cell Death Protein 1） Antibody in Recurrent/ Advanced Stage Endometrial Cancer Patients

Inclusion Criteria:

1. The subject understands the trial process, signs an informed consent form, and agreesto participate in the research
2. 18-70 years of age and female;
3. Histologically confirmed endometrial epithelial carcinoma (including endometrioidadenocarcinoma, clear cell carcinoma, serous adenocarcinoma,dedifferentiated/undifferentiated endometrioid carcinoma), carcinosarcoma (excludingspecific types of endometrial epithelial carcinoma such as small-cell neuroendocrinecarcinoma), and excluding uterine sarcoma；
4. Recurrence or advanced endometrial cancer that is not suitable for local treatment. Atleast first-line chemotherapy has failed or is intolerant；Including the following

• Patients with recurrent endometrial cancer have received at least first-linechemotherapy for recurrence, and imaging studies suggest disease progressionduring or after treatment
• Advanced endometrial cancer (FIGO Stage III-IV) that has received neoadjuvantchemotherapy/adjuvant chemotherapy or radical concurrent radiotherapy andchemotherapy, disease progression during first-line chemotherapy or recurrencewithin 6 months of the end of first-line treatment
• Patients with recurrent endometrial cancer cannot tolerate first-linechemotherapy

5. At least one measurable lesion by RECIST1.1 on CT;
6. Subjects provide formalin-fixed and paraffin-embedded tumor tissue samples forpathological consultation；
7. ECOG performance status 0-1;
8. Life expectancy ≥ 16 weeks;
9. Good organ function, including:

• Neutrophil count ≥1500/µL (no growth factor support treatment within 7 days ofthe start of the study treatment)
• Platelets ≥100,000/µL (Do not accept platelet transfusion and any form ofplatelet-increasing treatment within 2 weeks of the start of the study)
• Hemoglobin ≥90g/L (transfusion should not be received within 2 weeks from thebeginning of study treatment, and EPO should be required for support treatmentwithin 7 days)
• Serum creatinine ≤1.5 times the upper limit of normal, or creatinine clearance ≥60mL/min (according to the Cockcroft-Gault formula)
• Total bilirubin ≤1.5 times the upper limit of normal or direct bilirubin ≤1.0times the upper limit of normal
• AST and ALT ≤2.5 times the upper limit of normal, liver metastasis must be ≤5times the upper limit of normal
• Urinary protein ≤ (+), or 24-hour urine protein quantification is less than 1g
• Thyroid-stimulating hormone (TSH) ≤1xULN (if abnormal, also examine FT3, FT4, ifnormal, it can be included in the group)
• Plasma cortisol ≤1xULN
• International normalized ratio (INR) and activated partial thromboplastintime≤1.5ULN (unless anticoagulant therapy is being used due to disease)

10. The adverse effects of any previous treatment have returned to ≤CTCAE grade 1 orbaseline, except for symptomatically stable sensory neuropathy or hair loss ≤CTCAEgrade 2, except for anemia.
11. Previous hormonal or immunotherapy was permitted.
12. Women of reproductive age who had a negative pregnancy test at the time of enrolmentand who committed to use adequate and effective contraception or abstinence for theperiod from the beginning to the end of the study and for a period of 3 months afterthe last administration of the study medication were eligible for enrolment

Exclusion Criteria:

1. Prior receipt of any PARP inhibitor;
2. Patients with other invasive cancers other than endometrial cancer within the first 5years of enrollment, excluding complete treatment of various cancers in situ within 2years, such as squamous cell skin cancer, breast cancer, etc.
3. The last systemic or radical antitumor therapy, including radiotherapy, chemotherapy,and targeted therapy (small molecule targeted therapy is within 2 weeks before thefirst administration), immunotherapy, and palliative radiation therapy for symptomcontrol, was completed at least 2 weeks before the first administration.
4. Received Chinese patent medicines or Chinese herbal medicines or immunomodulatorydrugs (thymus, interferon, interleukin, etc.) with anti-tumor effects 2 weeks beforeenrollment.
5. Have undergone major surgery within 4 weeks before the start of the study or areexpected to undergo major surgery during the study period, or any surgical effectsthat have not yet recovered after the surgery.
6. Symptomatic, uncontrolled brain metastases or neumomeningeal metastases without theneed for radiographic confirmation;Patients with spinal cord compression may still beconsidered if they received targeted treatment and have evidence of clinically stable > for at least 28 days (controlled CNS metastases must have been treated withtreatment such as radiation or chemotherapy at least 1 month prior to studyentry;Patients should not develop new symptoms associated with central nervous systemlesions or symptoms indicative of disease progression, and patients should either takea steady dose of hormones or do not need hormones.)
7. Uncontrollable pleural and ascites.
8. Any active autoimmune disease or a history of autoimmune diseases (including but notlimited to: autoimmune hepatitis, interstitial pneumonia, enteritis, hepatitis,nephritis, the pituitary gland inflammation, vasculitis, uveitis, or need to acceptthe system of sex hormone therapy and/or immunosuppressive therapy in patients withasthma (such as the need of bronchodilator), except the following:In the last 2 yearswithout systematic treatment vitiligo, alopecia, Graves disease, psoriasis or eczema,stable immune thyroiditis controlled with treatment, type I diabetes requiring onlystable insulin, childhood asthma has been completely remission.
9. Immunosuppressant or systemic hormonal therapy (>10mg/ d or other equivalent hormonalpreparation) was being used for immunosuppressive purposes and continued to be used 2weeks before enrollment. Topical and systemic use not exceeding >10mg/ d or otherequivalent hormonal preparation was permitted.
10. With active bleeding (need) researchers to evaluate bleeding caused by tumor, withbleeding tendency or bleeding risk (such as tumor involving the great vessels,important bronchus, unable to control the obvious bleeding after hemostatic treatment,not cured bronchiectasis), or blood coagulation function apparently unusual, istreated with thrombolysis and anticoagulation (including need long-term antiplatelettherapy).
11. Thrombosis or embolism events in the past 6 months, such as cerebral vascular accident (including transient ischemic attack), pulmonary embolism;
12. Severe cardiovascular disease or medical history includes but not limited to thefollowing:

• NYHA (New York Heart Association) grade 3 and 4 congestive heart failure within 6months before enrollment.
• Suffered from unstable angina or newly diagnosed angina or myocardial infarctionwithin 12 months before screening.
• Arrhythmia requiring therapeutic intervention (Patients taking β-blockers ordigoxin can be included in the group).
• Valvular heart disease with CTCAE≥2.
• Poorly controlled hypertension (systolic blood pressure> 150 mmHg or diastolicblood pressure> 100 mmHg;

13. Patients with moderate or above pulmonary dysfunction that cannot be relieved,interstitial pulmonary disease or active pulmonary tuberculosis;
14. Patients with active ulcers, intestinal perforation, unmitigated intestinalobstruction, and a history of gastrointestinal perforation during the 28 days prior tostudy enrollment.
15. Active inflammatory bowel disease, uncontrollable nausea and vomiting, inability toswallow study medication, any gastrointestinal disease that may interfere with drugabsorption and metabolism;
16. Active infections such as human immunodeficiency virus, syphilis, untreated activehepatitis (HBV DNA copy number greater than 1000IU/ml, HCV RNA positive), etc.
17. Severe infection occurred 4 weeks before first administration;
18. Other serious or uncontrolled diseases.
19. Have received live vaccine or live attenuated vaccine 30 days before the firstadministration;
20. People who are known to be allergic to active or inactive ingredients of the studydrug or a drug with a similar chemical structure;Patients who are pregnant orbreastfeeding, or who are expected to become pregnant during the study treatmentperiod;
21. Other laboratory abnormalities:

• Uncorrectable hyponatremia (sodium <130 mmol/L; serum potassium <3.5 mmol/L);
• Any prior or current disease, treatment, or laboratory abnormality that mayinterfere with the results of the study and affect the patient's fullparticipation in the study, or that the investigator considers the patientunsuitable for participation in the study;

22. Any situation that the investigator deems unsuitable for participation, including poorunderstanding and coordination.