Elevated Bromide Levels Due to Tazemetostat Therapy Treated With Salt and Water Supplementation in Two Children With Atypical Teratoid Rhabdoid Tumor

Atypical teratoid rhabdoid tumor (ATRT) is an embryonal CNS tumor that afflicts young children. The molecular process associated with ATRT is loss of SMARCB1 or SMARCA4, which causes EZH2 overactivation. Tazemetostat hydrobromide is an EZH2 inhibitor, which has shown efficacy in the treatment of ATRT. Tazemetostat is produced as a bromide salt and can cause increased bromide levels that may require therapy cessation or dose reduction. We report two children with ATRT, who developed elevated bromide levels secondary to tazemetostat, which were treated with chloride. We propose consideration of salt supplementation in children receiving tazemetostat to prevent bromide elevation and pauses or reductions in therapy.