A Prospective, US-based Study Assessing Mogamulizumab-associated Rash in Patients Diagnosed With Mycosis Fungoides or Sezary Syndrome and Treated With Standard of Care Mogamulizumab

This study is being done to assess mogamulizumab-associated rash in patients diagnosed with mycosis fungoides or sezary syndrome and treated with standard of care mogamulizumab. One of the most common side effects of mogamulizumab is a rash, currently named mogamulizumab-associated rash (MAR) which can look like MF or SS. However, mogamulizumab-associated rash (MAR) does not indicate failure of mogamulizumab, and may be a sign that the drug is working. If not properly evaluated, mogamulizumab-associated rash (MAR) could be misinterpreted as worsening of mycosis fungoides/sezary syndrome, which could lead doctors to recommend stopping mogamulizumab treatment early. The information learned by doing this research study may help tell the difference between mogamulizumab-associated rash (MAR) (sometimes also called "drug eruption") and worsening of the disease. It may also help to uncover information about the cause of mogamulizumab-associated rash (MAR).

PRIMARY OBJECTIVE: I. To assess the incidence of mogamulizumab-associated rash (MAR) and its association with overall response in patients with cutaneous T-cell lymphoma (CTCL); mycosis fungoides \[MF\] and sezary syndrome \[SS\] subtypes) treated with mogamulizumab. OUTLINE: This is an observational study. Patients complete questionnaires, have photographs of their skin taken, and undergo blood sample collection and skin biopsies on study. Patients' medical records are also reviewed.