This is a prospective, open-label, single-arm, single-center study designed to evaluate the feasibility of using patient-derived organoid drug sensitivity analysis to guide chemotherapy for pediatric patients with refractory and relapsed malignant soft tissue tumors. The primary endpoint of the study is objective response rate (ORR), and the secondary endpoint is event-free survival (EFS).

This is a prospective, open-label, single-arm, single-center study with a planned total enrollment of 30 pediatric patients with refractory and relapsed malignant soft tissue tumors. Patients will be enrolled in this clinical trial after providing informed consent and meeting the inclusion and exclusion criteria. As this is a single-arm study without a control group, all patients will be assigned to the experimental arm. Treatment regimens will be comprehensively evaluated and adjusted based on the results of patient-derived organoid drug sensitivity testing in combination with clinical response. Clinical efficacy will be assessed during follow-up to evaluate the feasibility of using organoid drug sensitivity analysis to guide chemotherapy for refractory and relapsed malignant soft tissue tumors in children.

Inclusion Criteria:

1. Age between 1 and 18 years, gender unrestricted.
2. Patients with histopathologically confirmed rhabdomyosarcoma, Ewing sarcoma, malignant rhabdoid tumor, or non-rhabdomyosarcoma soft tissue sarcoma.
3. Previous receipt of at least one line of systemic anti-tumor therapy with subsequent disease progression.
4. Presence of measurable target lesions according to RECIST 1.1 criteria.
5. Sufficient biopsy tissue can be obtained from either metastatic or primary lesions.
6. ECOG performance status score of 0 to 1.
7. Expected overall survival ≥ 6 months.
8. Adequate bone marrow reserve: HB ≥ 90 g/L; ANC ≥ 1.5×10⁹/L; PLT ≥ 80×10⁹/L.
9. Adequate hepatic and renal function: total bilirubin ≤ 1.5 × upper limit of normal (ULN); ALT and AST ≤ 2.5 × ULN; serum creatinine ≤ ULN.
10. Voluntary participation in the study with signed written informed consent form (ICF), good compliance, and willingness to comply with follow-up procedures.

Exclusion Criteria:

1. Patients with peripheral nervous system disorders caused by the disease, or a history of significant psychiatric or central nervous system disorders.
2. Patients with severe infection or active peptic ulcer requiring treatment.
3. Patients currently participating in other clinical trials or who have participated within the past 3 weeks.
4. Patients deemed ineligible by the investigator for any other reason.