Abstract PO-102: A novel disseminated tumor cell identified in myriad cancer harbors tumor initiating properties

The identification of a disseminated tumor cell generated by heterotypic cell fusion, a circulating hybrid cell (CHCs) is a biologically relevant analyte of disease across myriad of cancers. Detected at elevated levels in peripheral blood, this novel population can be leveraged to understand mechanisms driving metastatic progression and predict metastatic spread. Our long term goal is to leverage evolving knowledge of mechanisms of metastatic progression to identify biologically relevant tumor markers for clinical disease assessment strategies. We therefore detected and delineated the role of CHCs as a measure of disease across a multitude of solid tumors. Human blood specimens were collected and analyzed with IRB approved protocols. Peripheral blood was obtained from patients with cancer in 14 different organ sites: ampullary adenocarcinoma, breast adenocarcinoma, cholangiocarcinoma, colon adenocarcinoma, esophageal cancer, high grade glioma (pediatric & adult), head and neck squamous cell carcinoma, pancreatic ductal adenocarcinoma, pancreatic neuroendocrine tumor, prostate adenocarcinoma, rectal adenocarcinoma and uveal melanoma and healthy subjects. Peripheral blood mononuclear cells were isolated and prepared for flow cytometry or immunofluorescence microscopy analyses with antibodies to CD45 and panCytokeratin, EpCAM, NKI Beteb, chromogranin A (CHGA)/synaptophysin (SYP) or glial fibrillary acid protein (GFAP). Discrete cellular populations including CHCs and circulating tumor cells (CTCs) were identified by protein expression. Cyclic immunofluorescence (cycIF) techniques were performed on a subset of specimens, for indepth interrogation of phenotypic heterogeneity in both the tumor and among CHCs. CHCs, defined by co-expression of CD45+ and a tumor associated protein were detected in all subjects across all disease sites at statistically significantly higher numbers than in controls samples using both detection paradigms. Furthermore, higher levels of CHCs compared with CTCs (that were CD45-) across disease sites. CycIF analysis of tumor tissue and dissemnated tumor cells from a triple negative breast cancer subject revealed a heterogeneous population of CHCs as well as complex tumor ecosystem. The phenotypic diversity of CHCs included CD44 and androgen receptor (AR) expression, which aligned with those detected in the proliferative tumor compartment. AR expression in triple negative breast cancer is known to correlate with treatment resistance and indeed, our subject rapidly succumb to disease. Taken together, these data suggest that tumors disseminate a heterogeneous population of CHCs that reflect the overall phenotype of viable tumor, supporting the value of phenotypically profiling CHCs for liquid biopsy to anticipate disease evolution and treatment resistance. This study established an isolation and detection platform for measuring CHCs in myriad of cancers and methods of phenotypic profiling CHC heterogeneity to identify discrete subpopulations. Citation Format: Matthew S. Dietz, Thomas Sutton, Brett Walker, Young Hwan Chang, Koei Chin, Melissa H. Wong. A novel disseminated tumor cell identified in myriad cancer harbors tumor initiating properties [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-102.