8530 Background: The consolidation treatment with durvalumab, an anti-PD-L1 antibody, after concurrent chemo-radiotherapy (CCRT) has become a new standard of care for locally advanced non-small cell lung cancer (LA-NSCLC). The rationale of the addition of anti-PD-L1 antibody is based on preclinical evidence suggesting that chemotherapy and radiotherapy may up-regulate PD-L1 expression on tumor cells. However, there has been reported no clinical evidence showing up-regulation of PD-L1 expression after CCRT. Methods: LA-NSCLC patients with paired sufficient histologic specimens for immune-histochemical analysis of tumoral PD-L1 expression (tumor proportion score, TPS) and stromal CD8-positive tumor-infiltrating lymphocyte density (CD8+density) before and after pre-operative treatment were eligible in this study. Twenty-three patients who underwent CCRT were reviewed in comparison with 18 patients who underwent chemotherapy. Results: PD-L1 expression was significantly enhanced after CCRT (median TPS, 48 from 1; P<0.01), but not after chemotherapy (median TPS, 7.5 from 1; P=0.62). No significant correlation between baseline TPS and TPS after CCRT (P=0.119). Stromal CD8+density was significantly increased after CCRT (median, 39 from 11; P<0.01) and after chemotherapy (median, 23 from 12; P<0.01). No significant correlation between baseline TPS and TPS after CCRT (P=0.378). Among CCRT cases, stromal CD8+density after treatment was significantly higher in cases with higher pathologic response to CCRT (median, 55 versus 27; P<0.01), and higher stromal CD8+density was a significant factor to predict a favorable survival after surgery (P=0.03 for recurrence-free survival; P=0.02 for overall survival). Conclusions: PD-L1 expression was significantly upregulated after CCRT regardless of baseline PD-L1 status, which may provide a pathologic rationale for the use of anti-PD-L1 agent after CCRT to improve the prognosis. Stromal CD8+density also increased after CCRT, which was correlated with pathologic response to CCRT and provided a significant prognostic impact.