Background: PD-L1 high expression and high tumor mutation burden (TMB) are reported to be correlated with high sensitivity to immune checkpoint inhibitor (ICI) in non-small cell lung cancer (NSCLC). This immuno-oncology biomarker study is ongoing as part of nationwide genomic screening by LC-SCRUM-Japan. Planned accrual is 1000 patients. Methods: Lung cancer patients enrolled in LC-SCRUM-Japan were primarily screened with targeted next-generation sequencing with Oncomine™ Comprehensive Assay (OCA) and monitored clinical course and survival every 6 months. To explore new biomarkers for ICI in the treatment of NSCLC, further analyses of 4 immunohistochemistry (IHC) assays for PD-L1 expression (22C3, 28-8, SP263 and SP142) and whole-exome sequencing (WES) to determine TMB level were conducted in 1000 and 400 patients, respectively. Results: Among 1635 patients with lung cancer enrolled in LC-SCRUM-Japan between Feb 2017 and Jan 2018, 621 NSCLC patients were enrolled in this immuno-oncology biomarker study. The results of PD-L1 IHC with 420 patients, OCA with 380 patients, WES with 50 patients, were analyzed at data cutoff point of Jan 4, 2018. Median TMB level by WES was 72 (2 to 515) and median TMB level by OCA was 7.6 mutation/Mb (0 to 30.8). There was no significant association between each PD-L1 expression and TMB by WES. TMB by OCA had a weak correlation with TMB by WES (R²= 0.31). Seventy-seven patients treated with ICI were evaluable for clinical response. Among 6 responders to ICI, TMB level by WES was various (19, 26, 26, 109, 144, and 249). Of these, 2 had both high TMB by WES (≥ median 72) and PD-L1 high expression; 2 had TMB low/PD-L1 high; 1 had TMB high/PD-L1 low: 1 had TMB low/PD-L1 low but high TMB by OCA (15.4 mutation/Mb). Conclusions: High TMB level appears to produce high sensitivity to ICI in patients with NSCLC, independent of PD-L1 high expression. Based on WES analyses in a large cohort, the findings to explore a precise predictive immuno-oncology biomarker to maximize the therapeutic benefits will be reported at the meeting.