Clinical Trial of SP-2577 (Seclidemstat) in Patients With Relapsed or Refractory Ewing or Ewing-related Sarcomas

Inclusion Criteria for All Patients * Age ≥ 12 years and weight ≥ 40 kg. * Karnofsky ≥ 70% for over ≥ 16 years old and Lansky ≥ 70% for under 16 years old, equivalent to Eastern Cooperative Oncology Group (ECOG) performance status Grade 0 or 1. * Life expectancy of greater than 4 months in investigator's opinion. * Willingness to provide tumor biopsies during screening and while on treatment. Optional for patients \< 18 years of age and patients enrolled in the Ewing sarcoma combination treatment arm. Biopsies can be exempt if deemed by the investigator that the biopsy is not medically feasible for the patient or the patient is unfit for the procedure. * Normal organ and marrow function as defined below: * absolute neutrophil count (ANC) ≥ 1.5 x 109/L * platelets ≥ 100 x 109/L; no transfusion 7 days prior to labs * total bilirubin ≤ 1.5 x upper limit of normal (ULN) or, in patients with Gilbert syndrome, total bilirubin \> 1.5 x ULN as long as direct bilirubin is normal * AST and ALT ≤ 3 x ULN * creatinine ≤ 1.5 x ULN OR creatinine clearance ≥ 60 mL/min/1.73 m2 for patients with creatinine levels above normal * Ability to understand and the willingness to sign a written informed consent document. Additional Inclusion Criteria for Ewing Sarcoma Combination Treatment Cohort * Patients must have a histologic confirmed diagnosis of Ewing sarcoma with a known EWSR1 translocation through local assessment that is relapsed or refractory and must have received at least o…