Abstract 1107: Cell-surface vimentin-positive macrophages like CTCs as novel biomarkers of metastatic gastrointestinal stromal tumors

Abstract Background: Gastrointestinal stromal tumors (GISTs) are the most common gastrointestinal tract sarcomas and are heavily infiltrated with tumor-associated macrophages (TAMs). Biomarkers specifically capturing circulating tumor cells (CTCs) that can be used to noninvasively determine the disease status in GIST patients have been lacking. Patients and Methods: To fill this gap, we captured both regular CTCs and TAMs from GIST patients' blood and tumor samples using our proprietary cell-surface vimentin (CSV) antibody 84-1 and the TAM markers CD14 and CD68 based on our previous established CTC detection method from 104 localized or metastatic sarcoma patients and 10 healthy donors. Also, freshly procured metastatic GIST tissues were obtained from four patients. Results: We defined a rare population of CSV+ macrophage-like CTCs (ML-CTCs) in metastatic GIST patients' blood samples with expression of CD14 and CD68 but not CD45. Also, we demonstrated CSV+ ML-CTCs to be tumor microenvironment-derived. Metastatic GIST patients had markedly higher numbers of CSV+ ML-CTCs than localized GIST patients and healthy blood donors. However, regular CTC counts could not predict metastasis of GISTs but could for other types of sarcoma. Notably, CSV+ ML-CTCs were represented as M1-like macrophages in their phenotype and function. Conclusions: CSV+ ML-CTCs are novel biomarkers for prediction of metastatic risk and therapeutic response in GIST patients. Routinely monitoring these cells will be an important approach to liquid biopsy analysis of GISTs. Citation Format: Heming Li, Qing H. Meng, Hyangsoon Noh, Neeta Somaiah, Keila E. Torres, Xueqing Xia, Izhar Singh Batth, Cissimol P. Joseph, Zachary A. Mulder, Ruoyu Wang, Shulin Li. Cell-surface vimentin-positive macrophages like CTCs as novel biomarkers of metastatic gastrointestinal stromal tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1107.