Phase II trial of atezolizumab (Anti-PD-L1) in the treatment of relapsed/refractory IIB/IVB mycosis fungoides/Sézary syndrome patients after previous systemic treatment. EORTC-1652-CLTG “PARCT”

Introduction: Treatment of advanced mycosis fungoides (MF) and Sézary syndrome (SS) is a challenge. In this international, multicenter, open-label phase II trial, we assessed the efficacy and safety of anti-PD-L1 atezolizumab in stage IIB-IV refractory/relapsed MF and SS. Materials and methods: Patients received atezolizumab 1200 mg IV Q3w for up to 1 year unless progression or withdrawal. The main study endpoints were overall response rate (ORR), progression-free survival (PFS), time to next systemic treatment (TTNT), and overall survival (OS). Results: A total of 26 patients were enrolled from seven countries. Seventeen patients met the inclusion criteria. At a median follow-up of 36.6 months, the ORR was 15.4 % in the intention to treat (ITT) and 17.6 % in the per protocol (PP) population, respectively. In the PP group, 58.8 % of patients, and in the ITT group, 53.9 % of patients achieved partial response or stable disease as their best outcome. One complete response was observed after 1 year. Median PFS was 3 months (95 % CI 1.4–4.9) in PP and 3.1 months (95 % CI 2.4–4.0) in ITT. Median OS was not reached for PP and was 22.3 months (20.0-NE) for ITT. Median TTNT was 5.9 months (2.8-NE) in PP and 6.2 months (3.1–14.8) in ITT. The most common grade ≥ 3 adverse events were fatigue (23.1 %) and infections (15.4 %), with two sepsis-related deaths. Atezolizumab was primarily discontinued due to disease progression (50 %). Conclusions: Atezolizumab shows moderate activity in pretreated refractory/relapsed MF and SS. Further studies are needed to identify reliable predictors of safety and treatment response.