GPC3 and synovial sarcoma: There are currently several clinical trials open to children with tumors that express HER2, NY-ESO, GD2, B7-H3, EGFR, and GPC3, and some promising results have already been reported, notably using HER2 CAR T cells, in which complete responses have been achieved in patients with osteosarcoma and rhabdomyosarcoma [20] and with NY-ESO-1+ synovial sarcomas treated with NY-ESO CAR T cells [28,29].