MRX-2843 monotherapy is being tested in adults with relapsed/refractory, advanced, and/or metastatic solid tumors (NCT03510104), and an ongoing trial in relapsed/refractory acute leukemia (NCT04872478) has enrolled patients down to age 12, paving the way for a future trial in adolescents and adult patients with EWS. Here, EWSR1 is linked to acute leukemia.