Duvelisib and Nivolumab for the Treatment of Stage IIB-IVB Mycosis Fungoides and Sezary Syndrome

Inclusion Criteria: * Patients must have histologically or cytologically confirmed MF or SS, stages IIB to IVB with measurable disease and/or detectable blood involvement based on the Global Cutaneous Lymphoma Response Criteria * Patients must have had at least one line of prior systemic therapy * Age \>= 18 years. Because no dosing or adverse event data are currently available on the use of duvelisib in combination with nivolumab in patients \< 18 years of age, children are excluded from this study * Eastern Cooperative Oncology Group (ECOG) performance status =\< 2 (Karnofsky \>= 50%) * Absolute neutrophil count \>= 1000/mcL * Platelets \> 75,000/mcL * Total bilirubin =\< 1.5 x institutional upper limit of normal (ULN) or =\< 5 x institutional ULN if with history of Gilbert's syndrome * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 3 x institutional ULN * Creatinine =\< 2.0 x institutional ULN * Patients with treated brain metastases are eligible if follow-up brain imaging after central nervous system (CNS)-directed therapy shows no evidence of progression * Patients with known history or current symptoms of cardiac disease, or history of treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac function using the New York Heart Association Functional Classification. To be eligible for this trial, patients should be class 2B o…