Inclusion Criteria
ECOG Performance Status of 0 or 1 within 28 days prior to registration for protocol therapy
Histological evidence of primary Stage III or IV or recurrent endometrial carcinoma who have had definitive surgery for endometrial cancer
Measurable disease according to RECIST v1.1 and obtained by imaging within 28 days prior to registration for protocol therapy
The subject must have recovered from the acute toxic effects of prior therapy
The subject must have completed prior radiation therapy at least 28 days prior to registration for protocol therapy
Subjects with recurrence must have a documented complete response upon completion of initial definitive therapy
No prior malignancy is allowed except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or other cancer for which the subject has been disease-free for at least 5 years
Female subjects must be of non-childbearing potential
Laboratory values must be obtained within 14 days prior to registration for protocol therapy
Exclusion Criteria
Subjects with carcinosarcoma
Subjects who have a solitary central pelvic recurrence which can be curatively resected
Hypersensitivity to pembrolizumab or any of its excipients
Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to registration for protocol therapy or who has not recovered from adverse events due to agents administered more than 4 weeks earlier
Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis
Treatment with any investigational agent within 28 days prior to registration for protocol therapy
Has known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies)
Active autoimmune disease that has required systemic treatment in past 2 years
Has received systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to registration for protocol therapy
Has a known history of active TB (Bacillus Tuberculosis)
Pulmonary conditions such as sarcoidosis, silicosis, idiopathic pulmonary fibrosis, or hypersensitivity pneumonitis
Has a history of (non-infectious) pneumonitis that required steroids or active, non-infectious pneumonitis
Evidence of interstitial lung disease
Has an active infection requiring systemic therapy with the exception of an uncomplicated urinary tract infection
Pre-existing peripheral neuropathy that is greater than or equal to Grade 2
Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent
Has a known active Hepatitis B or Hepatitis C
Has received a live vaccine within 30 days of registration for protocol therapy
History of solid organ or stem cell transplant requiring immunosuppressive medications