A phase I/II trial is currently investigating the combination of tazemetostat/pembrolizumab in patients with molecularly unselected, advanced urothelial carcinoma (Clinicaltrials.gov NCT03854474) and another trial is investigating tazemetostat alone in advanced solid tumors harboring an ARID1A mutation (Clinicaltrials.gov NCT05023655). The gene discussed is ARID1A; the disease is urothelial carcinoma.