332 – Poster| Volume 141, SUPPLEMENT 1, 138-139, June 2016

Improved clinical sensitivity detection of circulating tumor cell assays using a dual selection strategy in women with epithelial ovarian cancer

      Objectives: Little is known about the role of circulating tumor cells (CTCs) in epithelial ovarian cancer (EOC). Methods available for selecting and enumerating CTCs traditionally analyze cells based on expression of epithelial cell adhesion molecule (EpCAM) only. Fibroblast activation protein α (FAPα), a marker of activated stromal fibroblasts in tumors, is highly expressed in EOC. The goal of this study was to evaluate the sensitivity of adding FAPα as a selection marker for the isolation of CTCs in EOC, and to compare FAPα and EpCAM expressing CTCs in various subgroups of women with EOC.
      Methods: To isolate CTCs, we used 2 microfluidic chips in series, one with antibodies specific to cells bearing FAPα (CTCFAPα), the other to EpCAM (CTCEpCAM). For analysis, EOC patients were divided into 3 groups: patients with advanced-stage (III/IV) disease undergoing interval debulking after neoadjuvant platinum-based chemotherapy (A-EOC-chemo), patients with advanced-stage disease undergoing primary debulking without prior chemotherapy (A-EOC-no chemo), and patients with early-stage (stage I) disease. Blood specimens from 11 normal donors were also analyzed.
      Results: Sixteen patients with EOC were enrolled in this study, 8 A-EOC-no chemo, 5 A-EOC-chemo, and 3 stage I (Fig. 1). Median CTCEpCAM and CTCFAPα count was 121 and 31 for stage I, 214 and 58 for A-EOC-no chemo, 48 and 28 for A-EOC-chemo, and 0.1 and 0.3 for normal donors, respectively. EpCAM and FAPα antigens were not co-expressed in single CTCs. Using our dual selection strategy, the sensitivity of CTC detection was 100% for all cohorts, including stage I patients. A 3-fold decrease in median CTCEpCAM count was observed for A-EOC-chemo patients compared with A-EOC-no-chemo patients (P < .007), but no differences were seen in median CTCFAPα counts between these 2 groups.
      Conclusions: We found that FAPα is not co-expressed with EpCAM in CTCs, resulting in high clinical yields of CTCs and dramatically improving clinical sensitivity. In addition, CTCFAP is more resistant to conventional chemotherapy with paclitaxel/carboplatin than CTCEpCAM. Thus, CTCFAP may be a potential biomarker of chemoresistance in EOC, offering opportunities for unique clinical indications for CTCs that were not available using only CTCEpCAM as a biomarker.
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      Fig. 1Box Plot Data for CTCFAPα and CTCEpCAM Isolated from Blood of EOC Patients: Early Stage, Chemo Naïve, Advanced Stage, Chemo Naïve (A-EOC-no-chemo) and Advanced Stage, Following Chemotherapy Treatment (A-EOC-chemo). The solid lines in the box plots represent the median and the dotted line is the mean for the data shown.
      Table 1Average and median CTCFAPα and CTCEpCAM collected from EOC patients and normal donors.
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