The purpose of this surveillance is to assess the safety and efficacy of Poteligeo Inj. 20 mg (mogamulizumab) in routine clinical settings.

This post-marketing surveillance (PMS) is designed as an all-case investigation in accordance with the Korean Ministry of Food and Drug Safety (MFDS) re-examination requirements. It targets adult patients with mycosis fungoides (MF) or Sézary syndrome (SS) who have received at least one prior systemic therapy and are treated with mogamulizumab (POTELIGEO® Injection 20 mg) under the approved indication in Korea.

Primary Objective: To assess the safety of mogamulizumab for patients treated under the approved indication in Korea.

Secondary Objective: To assess the effectiveness of mogamulizumab for patients treated under the approved indication in Korea.

Exploratory Objective: To perform additional subgroup and exploratory analyses of effectiveness, including evaluation in special populations such as elderly patients, patients with renal or hepatic impairment, and those with a history of hematopoietic stem cell transplantation, treated under the approved indication in Korea

Inclusion Criteria:

1. Adults 19 years of age or older
2. Individuals who are confirmed to have received administration of the study drug for the purpose of "the treatment for adult patients with fungoidal granuloma or Sezary syndrome who have received one or more systemic therapies," or who are considered to require administration of the study drug in the investigator's opinion
3. Individuals who (or whose legally acceptable representatives) signed the Consent to Use of Personal Information of their own free will for participation in this use-result surveillance

Exclusion Criteria

1. Patients with hypersensitivity to any ingredients of this drug
2. Patients who intend to use this drug for non-approved indications
3. Patients who participated in a pre-market clinical trial of the study drug and received administration of the study drug

A person who has Mycosis fungoides and sezary syndrome.

There is not a plan to make IPD available.