Assessment of Safety and Efficacy of Poteligeo Inj. 20 mg (Mogamulizumab) Through Use-result Surveillance

This study is monitoring the real-world safety and effectiveness of a drug called mogamulizumab (brand name Poteligeo) in patients with two rare types of skin lymphoma: mycosis fungoides and Sézary syndrome. This is a post-approval safety monitoring study, not a randomized trial. **You may be eligible if...** - You are 19 or older - You have been diagnosed with mycosis fungoides or Sézary syndrome (two types of cutaneous T-cell lymphoma, a rare skin cancer) - You have already received at least one prior systemic therapy - You are currently receiving or are being considered for mogamulizumab (Poteligeo) as part of your standard care - You have given consent to have your personal health information used **You may NOT be eligible if...** - You have a known allergy to any ingredient in Poteligeo - You intend to use this drug for a purpose outside its approved use Talk to your doctor to see if this trial is right for you.