LAUSR

Dear Editor, Sarcomas represent a heterogenous group of tumors accounting for about 1% of cancer in adults and 15% in children [1]. However, despite adequate locoregional treatment, up to 40% of patients develop metastatic disease. Drugs used in the advanced setting have very limited efficacy, with a response rate of <10% and progression-free survival of <4 months and are mainly used for palliative purposes [1]. It is, therefore, important to monitor individual therapy responses to avoid inefficient therapy and unnecessary toxicity. Such monitoring is currently based on repeated CT imaging which may represent an important burden for patients with advanced disease [2]. Circulating tumor cells (CTCs) have been considered a potentially promising tool to monitor therapy response in cancer patients. The detection of CTCs in the peripheral blood has been associated with prognosis in several tumor types, including breast, colorectal, prostate and non-small cell lung cancer [3]. CTCs count changes during treatment may also be predictive of response to treatment [3]. Data related to sarcoma-derived CTCs are very limited. Indeed, flow cytometry-based technologies for detecting sarcomaCTCs are limited by the lack of a universalmarker. In this regard, the isolation by size of tumor cells (ISET) diagnostic technique, which relies on the tumor cellular size, which is larger than leukocytes, may represent an interesting approach for CTC enrichment and detection in patients with sarcoma [4, 5]. The aim of the study was to evaluate the prognostic relevance of CTCs in patients with soft-tissue sarcomas (STS) treatedwith systemic therapy in the neoadjuvant and advanced setting, Seventy-six patients with metastatic sarcoma were prospectively enrolled between July 2017 and December 2020 (Supplementary Figure S1). The study design and