New PROSPER Data Demonstrate Real-World Impact of Mogamulizumab on Symptoms and Health-Related Quality of Life in Mycosis Fungoides and Sézary Syndrome

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PRINCETON, N.J., June 29, 2026 (GLOBE NEWSWIRE) -- Kyowa Kirin, Inc., a wholly owned subsidiary of Kyowa Kirin Co. Ltd (TSE: 4151), today announced positive results from PROSPER, a real-world observational study of mogamulizumab in adults with mycosis fungoides (MF) or Sézary syndrome (SS). In the study, patients reported clinically meaningful improvements in skin symptoms (itch, flaking, and redness) and body temperature regulation as early as week 4, with improvements in sleep and health-related quality of life (HRQoL) starting at week 12. Improvements were sustained throughout the study period, with additional gains in HRQoL reported through week 48. "Cutaneous T-cell lymphoma can affect far more than just the skin, impacting how patients feel and function every day," said Professor Julia Scarisbrick, Principal Investigator, Honorary Professor of Dermatology, University Hospitals Birmingham NHS Foundation Trust. "These findings from the PROSPER study are encouraging because they show that in patients with MF or SS, mogamulizumab can help ease symptoms that affect everyday life, and those improvements can be long-lasting." Mycosis fungoides and Sézary syndrome are two sub-types of cutaneous T-cell lymphoma (CTCL), a rare form of non-Hodgkin lymphoma that primarily affects the skin, presenting as patches, plaques, tumors, or reddening of the entire skin, and may be associated with severe itching. The disease may spread to lymph nodes, blood, and/or other organs in some patients. "Clinical studies are stronger when they are shaped by the voices and lived experiences of people living with the disease," said Susan Thornton, study author and co-CEO, Cutaneous Lymphoma Foundation. "Collaboration between industry and the patient community is essential to designing studies that generate more relevant insights into symptom burden, quality of life, and the day-to-day treatment experience." Key PROSPER Findings The study included 73 patients with relapsed or refractory MF or SS (n=41 MF; n=32 SS). Patient-reported outcomes were collected at baseline and throughout the study using:

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