• Clinically meaningful improvements in skin symptoms reported as early as week 4 and sustained over the 48-week study period 
• Data presented at the 6th World Congress of Cutaneous Lymphomas meeting in Montreal, Canada

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:

• A CTCL-specific symptom diary assessing the severity of skin itch, pain, redness, and flaking, frequency of sleep problems, and difficulty regulating body temperature
• The MF/SS-CTCL-QoL questionnaire, which measured the impact of CTCL on daily life
• The Brief Fatigue Inventory (BFI), which assessed fatigue severity and its impact on daily functioning

Mean symptom scores (mean +/- standard deviation) improved from baseline to week 48 across key skin symptoms, including itch (−2.5 ±3.4), flaking (−3.1 ±3.5), redness (−3.1 ±3.5), and pain (−1.7 ±4.4). Clinically meaningful improvements in skin itch, flaking, and redness were observed as early as week 4, and improvements in pain by week 12   (i.e., exceeding the minimum important difference (MID)). These effects were sustained through week 48.

By week 48, 30% of patients reported at least a 2-point improvement in sleep, and 37% reported better body temperature regulation. Patients also showed significant, clinically meaningful improvements in disease-specific health-related quality-of-life scores (MF/SS-CTCL-QoL) beginning at week 12, with further gains through week 48. While fatigue scores changed little among patients with MF, patients with SS showed a significant improvement in total BFI scores, reaching the MID threshold at week 48.

“Studies like PROSPER show why real-world data generation matters, particularly in rare cancers like mycosis fungoides and Sézary syndrome,” said Angela Williams, PhD, Global Head of Health Economics and Outcomes Research at Kyowa Kirin. “These data help broaden understanding of the lived experience of patients and care partners with mogamulizumab treatment in everyday practice, including the impact on symptoms and quality-of-life that may not be fully reflected by outcomes collected in clinical trial.”

About PROSPER

The objective of the PROSPER (ClinicalTrials.gov ID NCT05455931) study is to gain insight into the experiences of patients with MF or SS receiving mogamulizumab in real-world clinical practice through the collection of patient-reported outcomes (PRO) data, enriched with qualitative data on disease and treatment experience. The study was designed with input from patients and caregivers to ensure patient-relevant outcomes were selected, and it was conducted in six countries across North America, Europe, and the Middle East, at 19 sites working with patients with MF or SS. Patients were followed for up to 50 weeks from study enrollment.

U.S. POTELIGEO (mogamulizumab-kpkc) Indication

POTELIGEO injection for intravenous infusion is indicated for the treatment of adult patients with relapsed or refractory mycosis fungoides (MF) or Sézary syndrome (SS) after at least one prior systemic therapy.

Important Safety Information

WARNINGS AND PRECAUTIONS

Dermatologic toxicity: Monitor patients for rash throughout the course of treatment. For patients who experienced dermatologic toxicity in Trial 1, the median time to onset was 15 weeks, with 25% of cases occurring after 31 weeks. Interrupt POTELIGEO for moderate or severe rash (Grades 2 or 3). Permanently discontinue POTELIGEO for life-threatening (Grade 4) rash or for any Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN).

Infusion reactions: Most infusion reactions occur during or shortly after the first infusion. Infusion reactions can also occur with subsequent infusions. Monitor patients closely for signs and symptoms of infusion reactions and interrupt the infusion for any grade reaction and treat promptly. Permanently discontinue POTELIGEO for any life-threatening (Grade 4) infusion reaction.

Infections: Monitor patients for signs and symptoms of infection and treat promptly.

Autoimmune complications: Interrupt or permanently discontinue POTELIGEO as appropriate for suspected immune-mediated adverse reactions. Consider the benefit/risk of POTELIGEO in patients with a history of autoimmune disease.

Complications of allogeneic HSCT after POTELIGEO: Increased risks of transplant complications have been reported in patients who received allogeneic HSCT after POTELIGEO. Follow patients closely for early evidence of transplant-related complications.

ADVERSE REACTIONS

The most common adverse reactions (reported in ≥10% of patients) with POTELIGEO in the clinical trial were rash, including drug eruption (35%), infusion reaction (33%), fatigue (31%), diarrhea (28%), drug eruption (24%), upper respiratory tract infection (22%), musculoskeletal pain (22%), skin infection (19%), pyrexia (17%), edema (16%), nausea (16%), headache (14%), thrombocytopenia (14%), constipation (13%), anemia (12%), mucositis (12%), cough (11%), and hypertension (10%).

You are encouraged to report suspected adverse reactions to Kyowa Kirin, Inc. at 1-844-768-3544 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Please see additional Important Safety Information in full Prescribing Information as well as Patient Information.

About Kyowa Kirin

Kyowa Kirin aims to discover and deliver novel medicines and treatments with life-changing value. As a Japan-based Global Specialty Pharmaceutical Company, we have invested in drug discovery and biotechnology innovation for more than 70 years and are currently working to engineer the next generation of antibodies and cell and gene therapies with the potential to help patients with high unmet medical needs, such as bone & mineral, intractable hematological diseases/hemato-oncology, and rare diseases. A shared commitment to our values, to sustainable growth, and to making people smile unites us across the globe.  You can learn more about the business of Kyowa Kirin at www.kyowakirin.com.

COR-US-POT-0015 June 2026

CONTACT:

Susan Thiele
Head of Therapeutic Communications, North America
[email protected]

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