Abstract 5603: Functional studies on viable circulating tumor cells (v-CTCs) and frequent expression of PD-L1 on v-CTCs in pancreatic cancer

Introduction: The analysis of CTCs as liquid biopsies provides the possibility to avoid invasive tissue biopsies, with obvious implications in cancer diagnostics and treatments. We tested new methods for v-CTCs detection in patients (pts) with pancreatic cancer (PC), and investigated the clinical potential of v-CTCs in prognosis. We analyzed the PD-L1(L1) expression in primary PC tumors, metastatic lymph nodes (LN) and v-CTCs. Pts and Methods: 7.5 ml of venous blood was collected from 39 PC pts, either upfront surgery (U group) or pre-treatment, consisted of Gem:800mg/m2; and S-1:80mg/m2 given concurrently with IMRT to 60Gy ((NACRT:N group). To detect v-CTCs, we employed a telomerase-specific replication-selective adenovirus expressing GFP. For U group, samples were obtained before/after resection. For N group, samples were obtained before/after NACRT and after resection. To distinguish between leucocyte and cells with either epithelial or mesenchymal origin, cells were stained by anti-CD45, anti-Cytokeratin and anti-Vimentin Abs. GFP-positive and CD45-negative cells were counted as v-CTCs. To assess L1 expression in PC tissues (PC tumors and LN) and on v-CTCs, L1 IHC kit (22C3, for tissues) and anti-human L1 mAb(MIH1, for CTCs) were employed. Results: U group: 24 pts aged 53~85 years (male/female=12/12) were enrolled. 24 pts underwent curative resection. No v-CTCs were detected in 6 pts at both before and after resection, and 5 of 6 pts survived without recurrence. V-CTCs were identified in 18 of 24 pts, and 13 of 18 pts developed liver metastasis. Marked decrease of CTC counts were seen after resection in 10 of 18 pts, but 9 pts developed recurrences. N group: 15 PC pts aged 44~77 years (male/female=4/11) were enrolled. 15 pts underwent curative resection. No v-CTCs at 3 sampling points were detected in 5 pts, and 5 pts survived without recurrences. V-CTCs was identified in 10 of 15 pts, and 4 out of 10 pts developed disease recurrence. Marked increase in CTC counts was observed after NACRT in 5 of 6 CTC-positive pts before NACRT, and 3 of 5 pts developed liver metastasis and died. NACRT may induce tumor cell dissemination into the blood circulation for CTC-positive pts. PD-L1 expression: L1 expression were assessed for 21 pts (U group:18, N group: 3). For PC tumors, L1 molecules were expressed in 12 pts and expression level of these pts were all low (57%, ≥50% [high]=0 pts, 1-49% [low]=12 pts {10%=6, 20%=4, 40%=2},