A Prospective, Single-arm Clinical Study of Liposomal Mitoxantrone Combination Regimen in the Treatment of Relapsed and Refractory Solid Tumors in Children, Adolescents and Young Adults

Main inclusion Criteria: 1. The patient fully understands this study, voluntarily participates and signs the informed consent form (ICF). 2. Age: children (6 - 12 years old), adolescents (13 - 18 years old) and young adults (19 - 24 years old) (CAYA). The expected survival time is \> 3 months. 3. Diagnosed with relapsed and refractory solid tumors by histopathology, and it is one of the following subtypes: (1) bone and soft tissue tumors; (2) neuroblastoma; (3) other types of solid tumors that the investigator deems eligible for enrollment. 4. There must be measurable tumor lesions by CT, enhanced CT, PET/CT or MRI. 5. Karnofsky score \> 50; ECOG score ≤ 2. 6. Bone marrow function: neutrophil count \> 1.5 × 10⁹/L, platelet count \> 75 × 10⁹/L, hemoglobin ≥ 80 g/L. 7. Liver and kidney function: serum creatinine ≤ 1.5 times the upper limit of normal value; AST and ALT \< 2.5 times the upper limit of normal value (for patients with liver invasion \< 5 times the upper limit of normal value); total bilirubin \< 1.5 times the upper limit of normal value (for patients with liver invasion \< 3 times the upper limit of normal value). 8. No history of myocardial infarction, unstable angina, severe unstable ventricular arrhythmia or any other arrhythmia requiring treatment, no history of clinically severe pericardial disease, or no electrocardiogram evidence of acute ischemic or active conduction system abnormality within 6 months before recruitment. Main exclusion Criteria: 1. Patients with known hypersensitivity to any component of the study drugs. 2. Patients with other malignant tumors that are not under control (except for basal cell carcinoma of the skin, in-situ breast/cervical cancer, and other malignant tumors that have been effectively controlled without treatment in the past five years). 3. Pregnant, lactating women and women of childbearing age who are unwilling to take contraceptive measures. 4. Other situations judged by the investigator as not suitable for participating in this study.