Mogamulizumab + Low-Dose Total Skin Electron Beam Tx in Mycosis Fungoides & Sézary Syndrome

Inclusion Criteria:

   - Stages 1B IV MF or SS

   - 1 prior standard of care therapy

   - Prior LD-TSEBT (> 3 months prior) and prior mogamulizumab is allowed, as long as
   progressive disease (PD) did not occur while on therapy, and did not discontinue due
   to toxicities

   - ≥ 18 years of age

   - The Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2

   - All clinically-significant toxic effects of prior cancer therapy resolved to Grade ≤ 1
   by the National Cancer Institute Common Terminology Criteria for Adverse Events,
   version 5.0 (NCI-CTCAE, v 5.0).

   - MF and a known history of non-complicated staphylococcus colonization/infection is
   eligible provided that stable doses of prophylactic antibiotics continue.

   - The following minimum wash-out from previous treatments are required, if applicable.

      - ≥ 4 weeks for retinoids, interferons, Vorinostat, romidepsin, pralatrexate, or
      other systemic anti-cancer/CTCL therapies

      - ≥ 2 weeks for phototherapy, local radiation therapy

      - ≥ 2 weeks for topical therapy (including topical steroid, retinoid, nitrogen
      mustard, or imiquimod)

      - ≥ 12 weeks for total skin electron beam therapy

      - ≥ 4 weeks for monoclonal antibodies; except > 12 weeks for alemtuzumab

      - Rapidly progressive malignant disease may be enrolled prior to above periods
      after discussion with the Protocol Director.

   - Adequate hematologic function

      - Absolute neutrophil count (ANC) ≥ 1,500 cells/μL (≥ 1,500/mm3); or if known bone
      marrow involvement, then ANC ≥ 1,000 cells/μL (≥ 1,000/mm3)

      - Platelets ≥ 100,000 cells/μL (≥ 100,000/mm3); or if known bone marrow
      involvement, then platelets ≥ 75,000 cells/μL (≥ 75,000/mm3).

   - Adequate hepatic function

      - Bilirubin ≤ 1.5 times the specific institutional upper limit of normal (ULN).
      Exception: If Gilbert's syndrome; then ≤ 5 times ULN.

      - Aspartate transaminase (AST) and alanine transaminase (ALT) each ≤ 2.5 x ULN; or
      ≤ 5.0 x ULN in the presence of known hepatic involvement by CTCL.

   - Adequate renal function

      - Serum creatinine ≤ 1.5 x ULN; or

      - Calculated creatinine clearance > 50 mL/min using the Cockcroft Gault formula.

   - If prior allogeneic hematopoietic stem cell transplant (HSCT), then must be free of
   graft vs host disease (GvHD) and receiving immunosuppressive therapy.

   - Women of childbearing potential (WOCBP) must have a negative pregnancy test.

   - WOCBP must agree to use effective contraception during the study and for 3 months
   after the last dose.

   - Male participants and their female partners of child bearing potential must be willing
   to use an appropriate method of contraception during the study and for 3 months after
   the last dose.

Exclusion Criteria:

   - MF with limited disease (Stage IA) or central nervous system (CNS) disease

   - Concomitant corticosteroid use. (with the exception that topical steroid and oral
   prednisone are allowed at ≤ 20 mg/day, if patient has been on a stable dose for at
   least 4 weeks prior to study treatment)

   - Pregnant or breastfeeding

   - Active autoimmune disease or history deemed by the investigator to be clinically
   significant

   - Known human immunodeficiency virus (HIV) positivity; known human T-cell lymphotropic
   virus (HTLV-1) infection; or active hepatitis B or C.

   - Active herpes simplex or herpes zoster. Those receiving prophylaxis for herpes and who
   started taking medication at least 30 days prior to the Screening Visit, and have no
   active signs of active infection, and whose last active infection was more than 6
   months ago, may enter the study, and should continue to take the prescribed medication
   for the duration of the study.