Prognostic impact of valemetostat in relapsed/refractory adult T‐cell leukaemia‐lymphoma

The prognosis for patients with relapsed/refractory (R/R) adult T-cell leukaemia-lymphoma (ATL) remains dismal. Recently, valemetostat, a dual inhibitor for enhancer of zeste homologue (EZH) 1 and 2, was approved in Japan for R/R aggressive ATL. However, there is no real-world data on the efficacy and prognosis of valemetostat. We therefore analysed clinical outcomes in 28 patients with R/R aggressive ATL who received valemetostat at three hospitals in Kumamoto Prefecture between February 2023 and January 2025. The overall response rate (ORR) and complete response (CR) rate were 54.2% and 33.3% respectively. With a median follow-up of 19.2 months (7.3-21.7) for surviving patients, the median survival time was 15.8 months and median progression-free survival (PFS) was 8.3 months. The probabilities of 1-year overall survival (OS) and PFS were 55.8% and 44.1% respectively. Furthermore, the probabilities of 1-year duration of response and duration of CR were 56.2% and 71.4% respectively. Notably, the probability of 1-year OS was 90.9% in patients who achieved CR/partial response (PR) ('responders') compared to 17.0% in patients who did not achieve CR/PR (p < 0.001). Thus, valemetostat has the potential to be a reliable therapy for patients with R/R aggressive ATL, especially for responders.