Randomized Phase 2 study of Adjuvant Chemotherapy vs Observation After Complete Resection of Stage III Soft Tissue Sarcomas

INTERVENTION: Drug : 1. Chemotherapy Group In the chemotherapy group, participants with sarcoma in the extremities started their chemotherapy regimen within four weeks after undergoing surgery and completing the RT; meanwhile, those with retroperitoneal sarcoma started receiving adjuvant chemotherapy within 4–8 weeks after surgery. Two different chemotherapy regimens were employed, and the appropriate regimen was chosen by the investigator based on the characteristics of the tumor, patient’s age, and medical history. 1) Doxorubicin monotherapy: 75 mg/m2 administered as a 60‐minute intravenous infusion, once (day 1) every three weeks with a total of si Xcycles 2) Doxorubicin + ifosfamide: 25 mg/m2 of doxorubicin + 2 g/m2 of ifosfamide administered intravenously for three days (days 1, 2, and 3) every three weeks with a total of si Xcycles * In cases of severe AEs, the regimen may be changed to doxorubicin monotherapy. 2.Observation Group Post Op within weeks 9 and 18 after randomization Every 12 weeks thereafter until 2 years Every 24 weeks until 5 years. CONDITION: Neoplasms PRIMARY OUTCOME: 2‐year RFS on observation group SECONDARY OUTCOME: survival rate, median, and 95% confidence interval, afety evaluation(CTCAE 5.0) INCLUSION CRITERIA: 1. Patients age 19–75 years 2. Patients who underwent complete resection of STS (extremity, trunk, or retroperitoneum) 3. Patients who underwent R0 resection (R0 resection through reoperation) 4. Patients with stage 3 STS (American Joint Committee on Cancer 8th ed.) 5. If STS develops in the extremities, patients who received =50 Gy of adjuvant radiotherapy before or after radical resection If the primary site of cancer is the extremities, only patients who completed radiotherapy are eligible. If the STS develops in the retroperitoneum, patients who underwent R0 resection without radiotherapy were considered eligible for analysis. 6. Patients with an Eastern Cooperative Oncology Group performance status (ECOG PS) score of 0–1 7. Patients with adequate hematologic, organ, and coagulation functions within two weeks (14 days) prior to randomization: ‐ Absolute neutrophil count (ANC) of =1.5 × 109/L. Granulocyte colony‐stimulating fac