CD99 and Ewing sarcoma: The neuroblastoma tumouroids demonstrated diffuse strong nuclear PHOX2B (Hata et al, 2015; Trochet et al, 2004) staining (Fig. 4A, right panel), Ewing sarcoma tumouroids showed circumferential membrane staining for CD99 (Ambros et al, 1991; Zollner et al, 2021) (Fig. 4B, right panel), and osteosarcoma tumouroids with nuclear SATB2 (Conner and Hornick, 2013; Milton et al, 2022) staining (Fig. 4C, right panel).