Cutaneous T-Cell Lymphoma (CTCL) has a chronic, relapsing course with patients undergoing multiple, consecutive therapies. Treatment aims at the clearance of skin disease, minimization of recurrence, prevention of disease progression and preservation of quality of life.

The treatment of CTCL is primarily determined by the disease extent. Prolonged complete remissions have been obtained with skin-directed therapies in early stage Mycosis fungoides (MF) (IA-IIA), whereas advanced stages CTCL (IIB-IVB) are often refractory to treatment and, thus, have an unfavorable prognosis.

Currently, there is no standard treatment option for CTCL, especially for advanced stages, and the optimal treatment sequence is still debated with a large variability in the therapeutic approach across countries. Patients with advanced-stage disease or refractory cutaneous CTCL should be treated with systemic therapies and, whenever possible, should be offered to participate in clinical trials. Currently, there is a urgent call for new treatments in CTCL with higher response rate and prolonged time to progression;

In this study, we propose a very innovative treatment schedule in which mogamulizumab is used before Total Skin Electron Beam therapy (TSEB) for systemic disease control and as a maintenance treatment after skin-directed therapy. We hypothesize that our regimen will show a more manageable toxicity profile than a combination treatment and allow for a long-term mogamulizumab administration.

Inclusion Criteria:

• Diagnosis of MF stage IB, IIA or IIB at registration, and MF stage should have never met criteria for stage IIIA or higher.
• Subjects who have failed (refractory or relapsed) at least one prior course of systemic therapy.
• All clinically significant toxic effects of prior cancer therapy to grade ≤ 1 according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0 (NCI-CTCAE, v.5.0), excluding the specifications required in the criteria 'Adequate haematological and organ function' below
• Males and female subjects ≥ 18 years
• WHO performance status 0-1
• Adequate haematological and organ function:
• absolute neutrophil count (ANC) ≥ 1.0 × 109/L
• platelets ≥ 75 × 109/L (≥ 75,000/mm3)
• bilirubin ≤ 1.5 × upper limit of normal (ULN) except for subjects with Gilbert's syndrome;
• aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 × ULN
• serum creatinine ≤ 1.5 × ULN or calculated creatinine clearance > 50 mL/min using the Cockcroft-Gault formula
• Subjects previously treated with anti-CD4 antibody or alemtuzumab are eligible provided a washout period ≥ 3 months and CD4+ cell counts ≥ 200/mm3
• Clinically normal cardiac function based on 12-lead ECG and above the institutional lower limit of normal for left ventricular ejection fraction assessed either by multi-gated acquisition scan or cardiac ultrasound
• Women of child bearing potential (WOCBP) must have a negative serum pregnancy test within 3 days prior to the first dose of study treatment
• WOCBP must agree to use effective contraception, defined as oral contraceptives, double barrier method (condom plus spermicide or diaphragm plus spermicide) or practice through abstinence from sexual intercourse during the study and for 6 months after the last dose.
• Male subjects and their female partners of child bearing potential must be willing to use an appropriate method of contraception defined as oral contraceptives, double barrier method (condom plus spermicide or diaphragm plus spermicide) or practice through abstinence from sexual intercourse (periodic abstinence, e.g., calendar, ovulation, symptothermal, post-ovulation methods and withdrawal are not acceptable methods of contraception) during the study and for 6 months after the last dose.
• Female subjects who are breast feeding should discontinue nursing prior to the first dose of study treatment and until 6 months after the last study treatment
• Before patient registration, written informed consent must be given according to ICH/GCP, and national/local regulations

Exclusion Criteria:

• Prior treatment with mogamulizumab, or any other anti-CCR4
• Prior TSEB
• Patients who received localised radiotherapy within 2 weeks prior to registration
• Patients who received any systemic therapy for MF within 4 weeks prior to registration.

Note: In case of rapid progression, if patient has recovered from all toxicities AND last dose occurred more than 5 half lives of the drug/treatment used, patient could be allowed to start earlier after consultation with medical monitor

• History of other malignancy in the past 5 years with the exception of treated carcinoma in situ of the cervix, localized prostate cancer with PSA <0.1, in-situ melanoma, and non-melanoma skin cancer
• History of severe allergic anaphylactic reactions to chimeric, human or humanized antibodies, or fusion proteins
• Known hypersensitivity to CHO cell products or any component of the mogamulizumab formulation (see section 6.1.1)
• Significant uncontrolled intercurrent illness including, but not limited to:
• uncontrolled infection requiring antibiotics;
• clinically significant cardiac disease (class III or IV of the New York Heart Association [NYHA] classification);
• unstable angina pectoris;
• angioplasty, stenting, or myocardial infarction within 6 months;
• clinically significant cardiac arrhythmia
• Have active sign of herpes zoster
• Patients with a history of autoimmune-related hypothyroidism who are on thyroid replacement hormone are eligible for the study.
• Patients with eczema, psoriasis, lichen simplex chronicus, with dermatologic manifestations only (e.g., patients with psoriatic arthritis are excluded) are eligible for the study provided all of following conditions are met:
• Rash must cover <10% of body surface area
• Disease is well controlled at baseline and requires stable use of low to mild potency topical corticosteroids for at least 4 weeks.
• No occurrence of acute exacerbations of the underlying condition requiring psoralen plus ultraviolet A radiation, methotrexate, retinoids, biologic agents, oral calcineurin inhibitors, or high potency or oral corticosteroids within the previous 4 months.
• Immunomodulatory drugs or high-dose systemic steroids for concomitant or intercurrent conditions other than T-cell lymphoma within 7 days of registration.

However, stable dose of a low dose systemic systemic corticosteroid (≤10 mg prednisone equivalent per day) or stable dose of a low potency topical corticosteroid for at least 4 weeks prior to the registration is permitted. Subjects may receive intra-articular, intraocular, inhalation or nasal corticosteroids. Initiation of treatment with corticosteroids or increase in dose while on study is not permitted except for the treatment of adverse events.

• Patients who are planned to receive stem cell transplantation
• Has a known history of Human T-lymphotropic virus 1 (HTLV-1), or human immunodeficiency virus (HIV) (test to be performed within 21 days of registration if allowed by local legislation)
• Has known active Hepatitis B or Hepatitis C
• Note: patient will be eligible if:
• Negative hepatitis B surface antigen (HBsAg) test at screening
• Negative total hepatitis B core antibody (HBcAb) test at screening, or positive total HBcAb test followed by a negative hepatitis B virus (HBV) DNA test at screening . The HBV DNA test will be performed only for patients who have a positive total HBcAb test.
• Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation
• Any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before registration in the trial