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

This study is combining two treatments — a drug called mogamulizumab (which targets certain immune cells) and low-dose radiation to the whole skin (called total skin electron beam therapy) — for patients with a type of skin lymphoma called mycosis fungoides or Sézary syndrome, to see if the combination works better than either alone. **You may be eligible if:** - You have stage IB–IV mycosis fungoides or Sézary syndrome - You have had at least one prior standard treatment - You are 18 or older and able to carry out light daily activities - Side effects from prior treatments have mostly resolved **You may NOT be eligible if:** - You stopped a prior treatment due to serious side effects from that exact treatment - You have unresolved significant side effects from prior cancer treatments - Your disease was actively progressing while on mogamulizumab or the skin radiation previously Talk to your doctor to see if this trial is right for you.