Extracorporeal Photopheresis and Mogamulizumab for the Treatment of Erythrodermic Cutaneous T Cell Lymphoma

Inclusion Criteria: * Documented informed consent of the participant and/or legally authorized representative * Assent, when appropriate, will be obtained per institutional guideline * Agreement to allow the use of archival tissue from diagnostic tumor biopsies * If unavailable, exceptions may be granted with study principal investigator (PI) approval * Age: \>= 18 years * Eastern Cooperative Oncology Group (ECOG) =\< 2 * Histologically confirmed mycosis fungoides (MF) or Sezary syndrome (SS). Safety lead-in: \>= stage IIB OR \>= stage IB-IIA folliculotropic/transformed MF. Phase 2: \>= stage IB * Stage of disease according to Tumor-Node-Metastasis-Blood (TNMB) classification * Pathology report must be diagnostic or be consistent with MF/SS criteria * SS is defined as meeting T4 plus B2 criteria; where the biopsy of erythrodermic skin may only reveal suggestive but not diagnostic histopathologic features, the diagnosis may be based on either node biopsy or fulfillment of B2 criteria * For MF where the histological diagnosis by light microscopic examination is not confirmed, diagnostic criteria that been recommended by the International Society of Cutaneous Lymphomas (ISCL) should be used. * Measurable disease per Modified Severity Weighted Assessment Tool (mSWAT) and/or Sezary count * Baseline skin biopsy taken within 6 months available for central review submission * Without bone marrow involvement: Absolute neutrophil count (ANC) \>= 1,500/mm\^3 (performed w…