This study employed an open single-group clinical laboratory design method (Simon Phase II study) to investigate the efficacy and safety of combining sirolimus with TIC chemotherapy (albumin-paclitaxel + isocyclophosphamide + carboplatin) in the treatment of children with recurrent/refractory vitellocystoma. AFP levels were assessed after each course of treatment, while imaging evaluations were conducted every two courses. The remission rate following chemotherapy in this single-group clinical trial was compared to that reported in the literature for treating recurrent/refractory yolk sac tumor, evaluating overall remission rate (ORR) and progresion-free survival rate (PFS) and overall survival (OS), as well as monitoring and recording chemotherapy-related side effects.

The planned treatment protocol comprised four cycles of the S-TIC regimen, which included sirolimus administered orally at a dose of 1 mg/m² from day 1 to day 21-28, nab-paclitaxel at a dose of 200 mg/m² on day 1, ifosfamide at a dose of 1200 mg/m² from day 2 to day 5, and carboplatin at a dose of 400 mg/m² on day 2. Additionally, mesna and sulfamethoxazole were prescribed to prevent hemorrhagic cystitis and Pneumocystis Jirovecii Pneumonia (PJP), respectively. Each cycle spanned a duration of three to four weeks. AFP levels were evaluated at the end of each cycle, and radiological assessments were conducted every two cycles. Surgical intervention decisions were made based on the results of these assessments.

Each treatment cycle spans 21 to 28 days (equivalent to every 3 to 4 weeks). Provided that the treatment criteria outlined in the study are satisfied, the second and subsequent cycles will commence on either the 22nd or 29th day. In the event of severe drug-related adverse reactions, treatment will be discontinued, and the patient will be classified as having PD. Tumor response assessment will entail the re-evaluation of AFP and LDH levels every cycle, alongside imaging examinations every two cycles. Should AFP levels demonstrate a continuous increase over two consecutive monitoring sessions following the initial treatment cycle, or if imaging results indicate tumor progression, a diagnosis of PD will be made, resulting in the termination of the clinical trial. For pediatric patients whose trials have been terminated, alternative anti-tumor therapies will be administered in accordance with their individual clinical conditions.

The study employed a Simon's two-stage optimal design with a one-sided alpha of 20% and 95% power to test the null hypothesis of ≤5% objective response rate (ORR) against the alternative hypothesis of ≥20% ORR. In the first stage, 10 patients were enrolled: if ≤1 patient achieved an objective response (CR/PR), the trial would be terminated for futility. Otherwise, enrollment would expand to a total of 32 patients. The regimen would be considered promising if ≥6 objective responses were observed in the final analysis. The median PFS and overall survival (OS) were estimated using the Kaplan-Meier method, implemented through the "survival" and "survminer" packages in R software (version 4.2.2). Correlations between OS and other endpoints were assessed at the patient level using Spearman's rank correlation coefficient (ρ).