This is a prospective, observational, non-interventional, international, multi-center, mixed methods study that will involve the integration of quantitative and qualitative data in patients with MF/SS treated with Poteligeo.

The PROSPER study aims to collect information about the experiences of patients with MF/SS receiving Poteligeo and of their caregivers in real-world clinical practice. The objective of this study is to generate patient-level data to provide insights into real world clinical practice and an understanding of treatment decisions, as well as to collect patient reported outcomes (PRO) data, enriched with qualitative data on disease and treatment experience and burden, to demonstrate the full impact of treatment and the relevant patient experience in real-world clinical practice. The study will be conducted 6 countries, including North America, United Arab Emirates and countries in Europe, at 19 sites known to treat and follow-up patients with MF/SS. Patients will be followed for up to 50 weeks from study enrollment.

Inclusion Criteria:

1. Patient aged ≥18 years
2. Confirmed diagnosis of MF/SS
3. Disease staging at enrollment has been completed
4. About to commence primary treatment with Poteligeo® as per reimbursed indication
5. Patient is willing and able to complete the symptom diary and PROs.
6. Patient is willing and able to provide written informed consent to participate in the study in a manner approved by Institutional Review Board(IRB)/ Independent Ethics Committee (IEC) and local regulations

Exclusion Criteria:

1. Patient unable to participate in all aspects of the study and/or does not agree to the collection of data from medical records
2. Patient currently participating in an interventional clinical trial

Approximately 80 patients with a confirmed diagnosis of MF/SS and about to commence primary treatment with Poteligeo as per reimbursed indication will be recruited from approximately 19 sites across North America, United Arab Emirates and Europe.