Treatment Response Prediction with Circulating Tumor Cell-Derived Organoids for Soft Tissue Sarcoma.

e23521 Background: Pharmacologic treatment for soft tissue sarcoma (STS) remains challenging. There is a lack to predict treatment responses to chemotherapy or targeted therapy to oncologic drivers. We hypothesize that circulating tumor cells may enrich cancer initiating cells and represent a window to probe personalized drug treatment response. In this study, we test if drug sensitivity profile of short-term culture of tumor organoids derived from circulating tumor cells (CTCs) correlates to clinical treatment response. Methods: From April 2019 to December 2020, 50 patients with biopsy-confirmed STS, who had either recurrent or metastatic tumors, were enrolled in a prospective observational study in Taipei Medical University Hospital. The median age of the patients was 47, and the top 3 diagnoses were leiomyosarcoma, aggressive fibromatosis and rhabdomyosarcoma. 74% of patients had metastatic diseases at the time of blood collection. Fifty-five blood samples were collected and processed for CTC organoid culture and drug sensitivity analysis (EVASelect, CancerFree Biotech, Taipei, Taiwan), which involves culturing nucleated blood cells on a binary colloid crystal-coated surface. Clinical response was evaluated using RECIST criteria 3 months after blood collection. The relationship between CTC viability and clinical response was analyzed using a contingency table and Chi-square analysis. Results: The success rate of CTC expansion was 87.2% (48/55), as defined by ATP abundance higher than 3000 U2OS cells after 18 days of culture. Clinical information from 32 of the 50 cases was eligible for analysis, and the results showed that CTC viability at a 70% cutoff correlated with clinical disease control at 3 months after blood collection. The odds ratio, sensitivity, specificity, and diagnostic accuracy were 12 (p = 0.036), 92.3%, 50%, and 79%, respectively. A demonstration of the interaction between this research and the Molecular Tumor Board (MTB) in the Taipei Medical University Healthcare System is presented through a case study of metastatic angiosarcoma and its correlation. Conclusions: The study highlights the potential of using CTC drug sensitivity as a biomarker for precision medicine in STS, despite limitations such as small sample size, short follow-up, and disease and treatment heterogeneity. Advancements in gene-based precision medicine have been made in the past decade, but only a small number of STS patients have seen benefits from it. This emphasizes the need for further research to thoroughly evaluate the potential of CTC drug sensitivity as a predictive biomarker in clinical practice. Key words: soft tissue sarcoma; circulating tumor cells; liquid biopsy; predictive biomarker; precision medicine.