In a recent phase 2 clinical trial (www.clinicaltrials.gov, NCT04102150, accessed on 30 January 2024), a dual EZH2 and EZH1 inhibitor, valemetostat, was used to treat patients with relapsed or refractory (R/R) ATLL. This evidence concerns the gene EZH1 and adult T-cell leukemia/lymphoma.