Inclusion Criteria:

          -  Histologically confirmed diagnosis of metastatic or recurrent uterine cancer
             (endometrial carcinoma, carcinosarcoma, clear cell carcinoma, leiomyosarcoma,
             undifferentiated sarcoma, high grade endometrial stromal sarcoma) by Memorial Sloan
             Kettering Cancer Center. Carcinosarcomas, endometrioid and clear cell carcinomas that
             appears to have arisen in the ovary/fallopian tube or peritoneum are also eligible.
             Recurrence should not be amenable to curative approaches such as surgical resection or
             chemoradiotherapy.

          -  Tumor is confirmed to be one of the following: 1. MSI-high, or 2. MMR-deficient, or 3.
             Hypermutated defined as ≥20 somatic mutations in the tumor by MSK-IMPACT

          -  One or more prior lines of cytotoxic treatment for advanced disease (prior hormonal
             therapy is not considered to count as prior lines of therapy)

          -  Measurable disease by RECIST 1.1 criteria

          -  No known CNS metastases

          -  ECOG Performance status 0-1

          -  ECOG Performance status 0-1

          -  WBC ≥ 2000/uL, ANC ≥ 1500/uL, PLT ≥ 100,000/uL, HGB ≥ 8 g/dL

          -  Serum creatinine ≤ 1.5 x ULN or creatinine clearance of ≥ 40mL/min by Cockroft-Gault
             formula

          -  AST (SGOT) and ALT (SGPT) ≤ 3 x ULN

          -  Total bilirubin ≤ 1.5 x ULN, except subjects with Gilbert's syndrome who can have
             total bilirubin ≤ 3.0 mg/dL

          -  Able to sign voluntary written informed consent

          -  Female, 18 years of age or older

          -  Available archival tumor tissue or patient is willing to undergo new biopsy

          -  Premenopausal women of child bearing potential must have a normal urine or serum
             beta-HCG prior to enrollment, and must agree to use effective contraception during
             treatment with nivolumab and for at least 5 months following the last dose of
             nivolumab.

        Exclusion Criteria:

          -  Disease eligible for potentially curative treatment with standard chemotherapy,
             surgical resection, or chemoradiotherapy.

          -  Known or suspected autoimmune disease, except for subjects with vitiligo, diabetes
             mellitus, resolved childhood asthma/atopy, residual hypothyroidism due to an
             autoimmune immune condition only requiring thyroid hormone replacement, psoriasis not
             requiring systemic treatment, or conditions not expected to recur in the absence of an
             external trigger.

          -  Serious uncontrolled medical disorder or active infection which would impair the
             ability of the subject to receive protocol therapy or whose control would be
             jeopardized by protocol therapy

          -  History of bowel obstruction, refractory ascites, or bowel perforation due to advanced
             disease within the past 3 months from start of study treatment.

          -  Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, anti-CTLA-4
             antibody or any other antibody or drug specifically targeting T cell co-stimulation or
             immune checkpoint pathways

          -  Patients who have a condition that requires systemic treatment with either
             corticosteroids within 7 days of enrollment (systemic corticosteroid therapy is
             defined as >10 mg daily prednisone or its equivalent); or who require other
             immunosuppressive medications within 14 days of study drug administration. Inhaled or
             topical steroids and adrenal replacement doses > 10 mg daily prednisone equivalents
             are permitted in the absence of active autoimmune disease.

          -  Prior history of malignancy or a concurrent malignancy, with the exception of
             cutaneous basal cell carcinoma or squamous cell carcinoma, superficial bladder cancer,
             or in situ carcinoma of the uterine cervix, prostate, or breast, unless a complete
             remission was achieved at least 3 years prior to study entry and no additional therapy
             is required or anticipated to be required during the study period

          -  Breastfeeding women, pregnant women

          -  Prisoners or subjects who are involuntarily incarcerated

          -  Subjects who are compulsorily detained for treatment of either a psychiatric or
             physical illness

               -  Positive test for hepatitis B virus surface antigen (HBV sAg) or hepatitis C
                  virus ribonucleic acid (HCV antibody) indicating acute or chronic infection (if
                  patient has documented Hepatitis B and C from within 6 months of enrollment,
                  these tests do not need to be repeated.)

          -  Known history of testing positive for human immunodeficiency virus (HIV) or known
             acquired immunodeficiency syndrome (AIDS)

          -  Known allergy or Adverse Drug Reaction to nivolumab, or a history of allergy to study
             drug components.