Abstract 603: Viable circulating tumor cells predict occult metastatic disease and prognosis, and aberrant expression of PD-L1 on viable CTC in pancreatic cancer
Authors: Tanemura Masahiro , Furukawa Kenta , Mikamori Manabu , Matsuura Yusuke , Matsumoto Kenichi , Asaoka Tadafumi , Urata Yasuo 
Published: July 2021

Abstract
[Introduction] CTCs as liquid biopsy are an emerging minimally invasive tool for cancer diagnosis, surveillance, and treatment. We tested novel methods for viable CTCs (v-CTC) isolation in the patients (pts) with pancreatic cancer (PC), and investigated the clinical potential of v-CTCs in prognosis. Furthermore, 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 prospectively from 39 PC pts, either upfront surgery (Up group) or pre-treatment, consisted of Gem:800 mg/m2; and S-1:80 mg/m2 given concurrently with IMRT to 60 Gy (NACRT:N group). To detect v-CTCs, we employed a telomerase-specific replication-selective adenovirous expressing GFP. For Up 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-CTC. To assess L1 expression in PC tissues (PC tumors and LN) and v-CTCs, L1 IHC kit (22C3, for tissues) and anti-human L1 mAb (MIH1,for CTCs) were employed.
[Results] Up 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 recurrence. N group: 15 PC pts aged 44~77 years (male/female=4/11) were enrolled. 15 pts underwent curative resection. No v-CTCs were detected in 5 pts, and all 5 pts survived without recurrence. V-CTCs was identified in 10 of 15 pts, and only 3 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. RT may induce tumor cell dissemination into the blood circulation for CTC-positive pts. PD-L1 expression: L1 expression were assessed for 21 pts (Up 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}, &lt;1% [negative]=9 pts). For metastatic LNs, metastatic LNs were observed in 14 pts and L1-positive expression in these LNs were detected in only 4 pts (28%, all low expression). On the contrary, the majority of detected v-CTCs clearly expressed L1 molecule (92 CTCs out of 103 detected CTCs were L1-positive=89 %).
[Conclusions] Viable CTC detection appears as a promising prognostic marker. Immunotherapy with anti-PD-1/PD-L1 Abs may effectively target v-CTCs to evade recurrence.
Citation Format: Masahiro Tanemura, Kenta Furukawa, Manabu Mikamori, Yusuke Matsuura, Kenichi Matsumoto, Tadafumi Asaoka, Yasuo Urata. Viable circulating tumor cells predict occult metastatic disease and prognosis, and aberrant expression of PD-L1 on viable CTC in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 603.