A Study of Pembrolizumab on the Tumoral Immunoprofile of Gynecologic Cancers

Inclusion Criteria: 1. Have histologically or cytologically confirmed gynecologic tumor of müllerian origin, specifically epithelial ovarian, fallopian tube, primary peritoneal, or uterine endometrial cancer. 2. Have disease amenable to surgical resection. 3. Be willing and able to provide written informed consent for the trial. 4. Be at least 18 years of age on day of signing informed consent. 5. Be willing to provide tissue from a newly obtained core or excisional biopsy of a tumor lesion. Subjects for whom newly-obtained samples cannot be provided (e.g. inaccessible or subject safety concern) may submit an archived specimen only upon agreement of the investigator. 6. Have a performance status of 0 or 1 on the ECOG Performance Scale. 7. Demonstrate adequate organ function as defined below. All screening labs should be performed within 10 days of study drug administration: 7a. ANC ≥ 1,500/mcL 7b. Platelets ≥ 100,000/mcL 7c. Hemoglobin ≥ 9 g/dL or ≥ 5.6 mmol/L without transfusion or EPO dependency (within 7 days of assessment) 7d. Serum creatinine ≤ 1.5 times the upper limit of normal or calculated creatinine clearance ≥ 60 mL/min for subject with creatinine levels \> 1.5 times institutional upper limit of normal 7e. Serum total bilirubin ≤ 1.5 times the upper limit of normal or direct bilirubin ≤ the upper limit of normal with total bilirubin levels \> 1.5 times upper limit of normal 7f. AST and ALT ≤ 2.5 times the upper limit of normal or ≤ 5 times the upper limit of normal for subjects with liver metastases 7g. Albumin \> 2.5 mg/dL 7h. International Normalized Ratio (INR) or Prothrombin Time (PT) ≤ 1.5 times the upper limit of normal unless subject is receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of anticoagulants 7i. Activated Partial Thromboplastin Time (aPTT) ≤ 1.5 times the upper limit of normal unless subject is receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of anticoagulants 8\. Female subjects of childbearing potential should have a negative urine or serum pregnancy within 72 hours prior to receiving the first dose of study medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. 9\. Female subjects of childbearing potential should be willing to use 2 methods of birth control or be surgically sterile, or abstain from heterosexual activity until planned hysterectomy/oophorectomy. Subjects of childbearing potential are those who have not been surgically sterilized or have not been free from menses for \> 1 year. Exclusion Criteria: 1. Is currently participating and receiving a study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 weeks of the study drug administration. 2. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to study drug administration. 3. Has a known history of active TB (Bacillus Tuberculosis) 4. Hypersensitivity to pembrolizumab or any of its excipients. 5. Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to agents administered more than 4 weeks earlier. 6. Has received prior chemotherapy, targeted small molecule therapy, or radiation therapy for the current gynecologic malignancy. NOTE: Subjects who have received treatment for a prior unrelated malignancy must have recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to a previously administered agent. NOTE: If subject received major surgery, they must have recovered adequately from the toxicity and/or complications from the intervention prior to starting therapy. 7. Has a known additional malignancy that is progressing or requires active treatment. Exceptions include basal cell carcinoma of the skin, squamous cell carcinoma of the skin that has undergone potentially curative therapy, or in situ cervical cancer. 8. Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Subjects with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least four weeks prior to study drug administration and any neurologic symptoms have returned to baseline), have no evidence of new or enlarging brain metastases, and are not using steroids for at least 7 days prior to study drug administration. This exception does not include carcinomatous meningitis which is excluded regardless of clinical stability. 9. Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. 10. Has known history of, or any evidence of active, non-infectious pneumonitis. 11. Has an active infection requiring systemic therapy. 12. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation for the full duration of the trial, or is not in the best interest of the subject to participate, in the opinion of the treating investigator. 13. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. 14. Is pregnant or breastfeeding. 15. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent. 16. Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies). 17. Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA \[qualitative\] is detected). 18. Has received a live vaccine within 30 days of planned start of study therapy. NOTE: Seasonal influenza vaccines for injection are generally inactivated flu vaccines and are allowed; however intranasal influenza vaccines (e.g., Flu-Mist®) are live attenuated vaccines, and are not allowed.