ALCAM: A Novel Surface marker on EpCAMlow Circulating Tumor Cells

Abstract: Background: Current strategies in circulating tumor cell (CTC) isolation in pancreatic cancer heavily rely on the EpCAM and cytokeratin cell status. EpCAM is generally not a good marker given its transitory change during EMT or TME. There is a need to identify other surface markers to capture the complete repertoire of PDAC CTCs. The primary objective is to charac-terize putative protein biomarkers on the CTCs’ surface expressing low or negligible levels of EpCAM to aid with the investigation of pancreatic cancer in patients with metastatic tumors. Methods: Flow cytometry and surface mass spectrometry was used to identify proteins ex-pressed on the surface of PDAC CTCs in culture. CTCs were grown under conditions of attach-ment and in co-culture with naïve neutrophils. Putative biomarkers were then validated in GEMMs and patient samples. Results: Surface proteomic profiling of CTCs identified several novel protein biomarkers. ALCAM was identified as a novel robust marker in GEMM models and in patient samples. Conclusions: We identified several novel surface biomarkers on CTCs expressed under differing conditions of culture among which, we validated expression of AL-CAM on patient CTCs.