A blood sample will be collected at baseline, prior to and at the end of each doxorubicin infusion (48- or 72-hour) and following completion of chemotherapy for osteosarcoma, ESFT, rhabdomyosarcoma or intermediate and high-risk non-rhabdomyosarcoma soft tissue sarcomas.cTn-T and NT-BNP will be measured at baseline, prior to and at the end of each doxorubicin infusion (48- or 72-hour) and following completion of chemotherapy for osteosarcoma, ESFT, rhabdomyosarcoma or intermediate and high-risk non-rhabdomyosarcoma soft tissue sarcomas.