Pembrolizumab in Treating Patients With Relapsed or Refractory Stage IB-IVB Mycosis Fungoides or Sezary Syndrome

Inclusion Criteria

• This trial will include subjects with stage IB-IVB MF/SS (maximal stage since diagnosis will determine eligibility), and who have relapsed, are refractory, or progressed after at least one standard systemic therapy; current disease stage at time of entry will also be documented but will not be used for eligibility
• Subjects must have the following minimum wash-out and adverse event (AE) recovery period from previous treatments without treatment between documentation of relapse/progression and enrollment of specifically:
• >= 2 weeks for local radiation therapy
• >= 4 weeks for systemic cytotoxic anticancer agents, anticancer investigational agents that are not defined as immunotherapy, or for tumor-targeting monoclonal antibodies (mAbs) with the exception of alemtuzumab for which the washout is at least 8 weeks
• >= 15 weeks for anti-cluster of differentiation (CD)137 or anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) (including ipilimumab or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways)
• >= 2 weeks from resolution (i.e., = = 2 weeks for retinoids, interferons, vorinostat, romidepsin, denileukin diftitox, and therapeutic doses of oral corticosteroids (physiologic replacement doses of oral corticosteroids are allowed, topical corticosteroids are allowed)
• >= 2 weeks for phototherapy
• >= 1 week for topical therapy (including retinoid, nitrogen mustard, or imiquimod)
• Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) performance scale
• Life expectancy of at least 6 months
• Performed within 10 days of treatment initiation: Leukocytes >= 2,000/mcL
• Performed within 10 days of treatment initiation: Absolute neutrophil count >= 1,500/mcL
• Performed within 10 days of treatment initiation: Platelets >= 100,000/mcL
• Performed within 10 days of treatment initiation: Hemoglobin >= 9 g/dL OR >= 5.6 mmol/L
• Performed within 10 days of treatment initiation: Serum total bilirubin = 1.5 ULN
• Performed within 10 days of treatment initiation: Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]) and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) = = 60 mL/min for subject with creatinine clearance (CrCl) levels > 1.5 x institutional ULN (glomerular filtration rate [GFR] can also be used in place of creatinine or CrCl)
• Performed within 10 days of treatment initiation: International normalized ratio (INR) or prothrombin time (PT) = 1 year
• Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician immediately; men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of MK-3475 administration
• Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria

• Patients who have had chemotherapy or targeted small molecule therapy within 4 weeks (6 weeks for nitrosoureas or mitomycin C) prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier
• Note: patients with = = 45 years of age and has not had menses for greater than 1 year will be considered postmenopausal), or 3) not heterosexually active for the duration of the study; the two birth control methods can be barrier method or a barrier method plus a hormonal method to prevent pregnancy; patients should start using birth control from the time of the pre-study visit, through the course of the study and for 120 days after the last dose of study medication; the following are considered adequate barrier methods of contraception: diaphragm, condom (by the partner), copper intrauterine device, sponge, or spermicide; appropriate hormonal contraceptives will include any registered and marketed contr