Apostream, An Antibody-Independent Platform, Compared To Cellsearch For Enumeration Of Circulating Tumor Cells (Ctcs) In Patients With Metastatic Prostate Cancer

e21058 Background: Development of CTC detection platforms is a rapidly advancing field. The CellSearch technique relies on cell surface expression of EpCAM to select for rare tumor cells in whole blood specimens. Consequently, the use of EpCAM-based enrichment platforms to recover CTCs is limited to EpCAM expressing cells and is poorly suited for recovery of EpCAM negative cells like those having undergone epithelial mesenchymal transition (EMT). ApoStream is an antibody independent enrichment platform which utilizes the principle of continuous flow dielectrophoresis field-flow fractionation (DEP-FFF) to isolate and enrich for CTCs. A head to head comparison of CellSearch to ApoStream for recovery of CTCs in patients with metastatic prostate cancer was performed. Methods: Two 7.5 mL bloodsamples were collected at a single time point for each patient with stage IV prostate cancer. One sample was analyzed by CellSearch CTC enumeration kit, and one sample was analyzed by ApoStream. CTCs recovered by both devices were immunophenotyped using antibodies against cytokeratin (CK), CD45 and DAPI. CTCs were defined as CK+/CD45-/DAPI+ intact cells. CTCs recovered by ApoStream were further analyzed by quantitative laser scanning cytometry (LSC). A paired t-test was used to compare the cell counts in the two devices. Results: The ApoStream CTC enrichment platform isolated a greater number of CTCs from blood of eight patients compared to CellSearch (p= 0.0027). All cell counts obtained by the ApoStream technique were higher than CellSearch, and all patients had detectable CTCs by ApoStream, while only 75% of patients had detectable CTCs with CellSearch. Conclusions: The ApoStream platform is differentiated from EpCAM dependent platforms and is well suited for detection and recovery of CTCs in advanced stage disease where tumor cell heterogeneity is common and expression of EpCAM may be low or lost. [Table: see text]