Pembrolizumab in Treating Patients With Stage IB-IV Mycosis Fungoides

Inclusion Criteria

• Age >= 18 years
• Histological confirmation of one of the following:
• Stage IIB-IV mycosis fungoides not previously treated with systemic therapy
• Stage IB/IIA mycosis fungoides with Modified Severity Weighted Assessment Tool (mSWAT) >= 20 with high risk morphologic features defined as thick plaque disease and/or follicular involvement who have failed one form of skin-directed therapy.
• Sezary syndrome patients not previously treated with systemic therapy.
• Measurable disease based on mSWAT and/or Response Evaluation Criteria in Solid Tumors (RECIST) 1.1.
• Be willing to provide tissue from a newly obtained core or excisional biopsy of a tumor lesion. Note: Newly-obtained is defined as a specimen obtained up to 6 weeks (42 days) prior to registration. Exception: Subjects for whom newly-obtained samples cannot be provided (e.g. inaccessible or subject safety concern) may submit an archived specimen only upon agreement from the Sponsor.
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0 or 1.
• Absolute neutrophil count (ANC) >= 1, 500 /mcL (obtained = = 100,000/mcL (obtained = = 9.0 g/dL or >= 5.6 mmol/L without transfusion or erythropoietin (EPO) dependency (within 7 days of assessment)
• Serum total bilirubin = 1.5 ULN (obtained = 2.5 mg/dL (obtained = = 60 ml/min for subject with creatinine levels > 1.5 x institutional ULN (obtained =< 28 days prior to registration)
• Prothrombin time (PT)/international normalized ratio (INR) and partial thromboplastin time (PTT) =< 1.5 X ULN OR if patient is receiving anticoagulant therapy and PT/INR or PTT is within therapeutic range of intended use of coagulants (obtained =< 28 days prior to registration)
• Negative urine or serum pregnancy test done =< 28 days prior to registration and =< 72 hours prior to receiving the first dose of study medication, for women of childbearing potential only.
• Female subjects of childbearing potential must be willing to use an adequate method of contraception for the course of the study through 120 days after the last dose of the study medication.
• Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the subject.
• Male subjects of childbearing potential must agree to use an adequate method of contraception for the course of the study through 120 days after the last dose of the study medication.
• Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the subject.
• Provide written informed consent.
• Willing to return to enrolling institution for follow-up (during the Active Monitoring Phase of the study).
• Willing to provide tissue samples for correlative research purposes.

Exclusion Criteria

• Any of the following because this study involves: an agent that has known genotoxic, mutagenic and teratogenic effects:
• Pregnant women
• Nursing women
• Men or women of childbearing potential who are unwilling to employ adequate contraception
• Is currently participating and receiving study therapy or have participated in a study of an investigational agent and received study therapy or used an investigational device =< 4 weeks prior to registration.
• Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy =< 7 days prior to registration.
• Has a known history of active TB (Bacillus tuberculosis).
• Hypersensitivity to pembrolizumab or any of its excipients.
• Has had a prior anti-cancer monoclonal antibody (mAb) =< 4 weeks prior to registration or who has not recovered (i.e., =< grade 1 or at baseline) from adverse events due to agents administered more than 4 weeks earlier.
• Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy =< 2 weeks prior to registration or who has not recovered (i.e., =< grade 1 or at baseline) from adverse events due to a previously administered agent.
• Note: Subjects with =< grade 2 neuropathy are an e