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.

Inclusion Criteria:

• * Adult patients (>= 18 years of age) diagnosed with relapsed/refractory Mycosis Fungoides (MF) stage IB, IIA, IIB, III and IV or Sezary Syndrome(SS), and selected by their treating physician to receive single agent mogamulizumab (newly initiated)

  • Signed informed consent
  • Willing to undergo baseline biopsy and during treatment to evaluate for Mogamulizumab-Associated Rash (MAR) if clinically indicated
  • Willing to provide blood sample at baseline, and if applicable, at onset of Mogamulizumab-Associated Rash (MAR)

Exclusion Criteria:

• * Other concomitant systemic and skin directed Cutaneous T-cell Lymphoma (CTCL) regimens except for topical steroids

  • Prior treatment with mogamulizumab

Patients diagnosed with relapsed/refractory Mycosis Fungoides (MF) stage IB, IIA, IIB, III and IV or Sezary Syndrome(SS), and selected by their treating physician to receive single agent mogamulizumab (newly initiated).