EWSR1 and osteosarcoma: Interestingly, similar to the adult population, the principal OSTJS histotype in the pediatric age group was osteosarcoma (8, 53.3%; Fig. 2B), followed by Ewing sarcoma (4, 26.7%) and 1 each (6.7%) of rhabdomyosarcoma with TFCP2::EWSR1 rearrangement (Fig. 6A-F), mesenchymal chondrosarcoma, and alveolar soft part sarcoma.