Ludmilla T Domingos Chinen,1 Celso A Lopes Mello,2 Emne Ali Abdallah,1 Luciana MM Ocea,1 Marcilei E Buim,1 Natália M Breve,1 José Luiz Gasparini Junior,1 Marcello F Fanelli,2 Patrizia Paterlini-Bréchot3 1International Research Center, 2Department of Clinical Oncology, AC Camargo Cancer Center, São Paulo, Brazil; 3Unité INSERM U807, Université Paris Descartes, Paris, France Background: Sarcomas are rare and heterogeneous neoplasms with poor prognosis that are thought to spread to distant organs mainly by hematogenous dissemination. However, circulating tumor cells (CTCs) have never been visualized in sarcomas. Objectives: To investigate the feasibility of using isolation by size of tumor cells (ISET) for isolation, identification, and characterization of CTCs derived from patients with high-grade and metastatic sarcomas. Patients and methods: We studied eleven patients with metastatic/recurrent or locally advanced soft-tissue sarcomas (STSs), six of whom had synovial sarcomas. Blood samples (8 mL) were collected from patients with advanced STS and treated by ISET, a marker- independent approach that isolates intact CTCs from blood, based on their larger size compared with leukocytes. CTCs were identified by cytomorphology and characterized by dual-color immunocytochemistry using antivimentin or anti-Pan CK, and anti-CD45. Results: All patients with STS included in this study showed CTCs, with numbers ranging from two to 48 per 8 mL of blood. Conclusion: This study shows the feasibility of isolating, identifying, and characterizing CTCs from patients with different types of sarcomas and the presence of circulating sarcoma cells in all the tested patients. Our results set the basis for further studies aimed at exploring the presence, number, and immunomolecular characteristics of CTCs in different types of sarcoma, and bring more light to the mechanisms of tumor invasion for these tumors. Keywords: sarcoma, circulating tumor cells, ISET