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11541 Background: PD-L1 expression on tumor tissue is associated with response to PD-1 blockade in NSCLC. Here, we conducted a serial evaluation of PD-1-expressing circulating tumor cells (CTCs) as a potential real-time diagnostic modality in NSCLC patients treated with nivolumab. Methods: Advanced NSCLC patients after failure of at least one prior chemotherapy regimen received nivolumab monotherapy (3mg/kg, q2W) until progressive disease (PD) or unacceptable toxicity. Peripheral whole blood (3 mL) was collected for CTC evaluation at baseline and at week 4. CTCs were detected using microcavity array system (Hitachi Chemical Co., Ltd, Chikusei, Japan). PD-L1 expression was immunohistochemically examined on both tumor tissues and CTCs. This study was registered at UMIN (ID: 000024414). Results: Thirty patients were registered in the study between January 2016 and September 2016 at Wakayama Medical University Hospital and 29 were included in the analysis. Demographics of the patients were as follows: median age 70 (range, 49 to 86); male 73 %; stage IV, 100 %; squamous/non-squamous, 27/73 %. At baseline, CTCs were detected in all patients (median, 15; range, 1 to 90) and PD-L1-expressing CTCs were detected in 87% of patients. Tumor proportion score (TPS) of PD-L1 expression on CTCs ranged from 6% to 100%, indicating intrapatient heterogeneity. Matched tumor tissues were available from 14 patients and 7 showed the PD-L1 TPS ≥ 50%. No positive correlation was observed on PD-L1 expression between tumor tissues and CTCs based on TPS (R2 = 0.0035). Overall response rate was 25% (7/29), and disease control rate was 54% (15/29). Total CTC count was significantly decreased after nivolumab treatment at week 4 (p < 0.05), but no significant change was observed in PD-L1 TPS on CTC. Patients harboring CTCs with PD-L1 TPS 50% or more at baseline were significantly more likely to achieve non-PD than those harboring CTCs with TPS less than 50% (p < 0.05). Conclusions: This is the first report on a serial monitoring of PD-L1 expression on CTCs in patients treated with nivolumab. PD-L1-expressing CTCs are suggested to hold potential for predicting clinical benefit. Clinical trial information: 000024414.

e23036Background: Immune-checkpoint blockage with anti-PD-1 antibodies is effective against human malignancies including lung cancer. Although the expression of PD-L1 on tumor cells is expected as ...