RecruitingPhase 1Drug trialTegavivint With Gemcitabine in Patients With Relapsed or Refractory OsteosarcomaThe goal of this clinical trial is to define the maximum tolerated dose (MTD) and/or Recommended phase 2 dose (RP2D) of Tegavivint in combination with Gemcitabine in patients with relapsed or refractory osteosarcoma (OS). The study will also investigate the toxicities of Tegavivint in combination with gemcitabine in patients with relapsed or refractory OS.