Clinical significance of viable circulating tumor cells (v-CTCs) and PD-L1 expression in pancreatic cancer patients using a novel oncolytic virus system

Background: Detecting circulating tumor cells (CTCs) as a peripheral blood liquid biopsy is a promising approach. We previously succeeded in visualizing viable-CTCs (v-CTCs) with high biological activity from the peripheral blood of resectable and borderline resectable pancreatic cancer (PC) patients using a novel telomerase-specific oncolytic virus (TelomeScan F35). This study aimed to analyze the clinical significance of v-CTC detection and the expression of PD-L1 on v-CTCs in PC patients to explore potential therapeutic selection strategies. Methods: Thirty-nine PC patients were analyzed. CTCs were analyzed at pre-/post-operative time points in the Upfront Surgery (S) group, and at pre-NACRT, post-NACRT, and post-operative time points in the Neoadjuvant Chemoradiotherapy (NACRT) group (RT + GEM + S-1). PD-L1 expression was also assessed in v-CTCs, primary tumors and metastatic lymphnodes. Results: [S Group] (n=24; M/F=12/12; median age 73). All patients underwent curative resection. Six patients were consistently v-CTC negative (pre- and post-op); five of these patients remained disease-free, with only one case of peritoneal recurrence. In contrast, 18 patients were v-CTC positive at either or both time points; 13 of these developed early distant metastatic recurrence post-surgery. [NACRT Group] (n=15; M/F=4/11; median age 67). All patients underwent curative resection. Five patients were consistently v-CTC negative at all three time points and all remain disease-free. In six patients who were v-CTC positive pre-NACRT, the v-CTC count significantly increased post-NACRT in five cases, and three of them developed early liver metastasis, suggesting that RT might induce v-CTC intravasation/dissemination. [PD-L1 Expression] PD-L1 analysis was performed on 18 patients in the S group and 3 in the NACRT group. In primary tumors of the S group, PD-L1 expression was observed in 0%/10%/20%/40% of tumor cells in 6/6/4/2 cases, respectively. The expression rate on v-CTCs was 97% pre-operation and 81% post-operation. Among 12 patients with lymph node metastasis, PD-L1 expression was positive in only 4 cases (33%). In the NACRT group, primary tumors were all PD-L1 negative. The expression rate on v-CTCs was 50% pre-NACRT, 96% post-NACRT, and 50% post-operation. Two cases showed lymph node metastasis, both PD-L1 negative. Conclusion: The presence of v-CTC dissemination suggests a risk of metastasis development following NACRT, advocating for upfront surgery or neoadjuvant chemotherapy (NAC) without RT in v-CTC positive patients. Given the high rate of PD-L1 expression on v-CTCs, immune checkpoint inhibitors are expected to be effective for targeting v-CTCs and controlling distant metastasis. Detection of v-CTC dissemination may be utilized for therapeutic selection in PC patients.