Circulating Tumor Cells in Soft Tissue Sarcoma: Current Evidence and Clinical Implications

Soft tissue sarcomas (STS) comprise a rare and highly heterogeneous group of mesenchymal-derived malignancies, accounting for less than 1% of all cancers and characterized by diverse histologic and molecular subtypes. Despite their low incidence, STS account for a disproportionate burden of cancer-related morbidity and mortality, largely driven by their risk of metastatic dissemination. Early detection of metastatic spread is a cornerstone of preoperative staging, treatment planning, and postoperative monitoring in patients with STS. Although conventional imaging modalities remain fundamental for surveillance of metastatic disease, they may fail to accurately detect metastatic sites and provide limited insight into tumor biology. Advances in precision medicine have positioned liquid biopsy as a minimally invasive approach for the analysis of tumor-derived material, facilitating characterization of tumor biology and identification of prognostic biomarkers. Circulating tumor cells (CTCs) represent intact and viable tumor cells that provide unique genomic and phenotypic traits that could not be assessed using acellular tumor-derived material. They have emerged as promising biomarkers for monitoring disease progression, assessing treatment response, and stratifying prognosis. Particularly, their clinical value as prognostic biomarkers has been established in epithelial-derived malignancies. Despite these advances, the role of CTCs in STS remains largely investigational, mainly due to STS heterogeneity and the lack of standardized protocols for detection across platforms. Therefore, this narrative review summarizes the biomolecular mechanisms underlying CTCs in STS, including the role of phenotypic plasticity in tumor intravasation, anoikis resistance and its interaction with the tumor microenvironment, and stem cell-like phenotypes in tumor initiation at distant sites. Furthermore, we discuss current methodologies for CTC detection, highlighting emerging approaches developed to address the limitations of conventional methods. Finally, we provide a critical overview of subtype-specific detection strategies, as well as their clinical implications in treatment response monitoring and prognostic assessment.