Encouraging preclinical evidence led to a phase 1 clinical trial (NCT02601937) examining tazemetostat monotherapy in pediatric patients with relapsed or refractory SMARCB1 (also known as INI1) negative tumors, such as malignant rhabdoid tumors (MRT), including AT/RT, or other SMARCB1-deficient tumors and synovial sarcoma. The gene discussed is SMARCB1; the disease is synovial sarcoma.