INTRODUCTION: Use of pembrolizumab as first-line treatment in patients with non-small cell lung cancer (NSCLC) with PD-L1 tumor proportion score (TPS) ≥ 50 % was approved in Japan 5 years ago. We investigated the long-term efficacy and safety of this treatment in a real-world setting. METHODS: This multicenter observational study enrolled 95 consecutive cases of histologically diagnosed advanced or recurrent NSCLC with a PD-L1 TPS score ≥ 50 %, who received pembrolizumab as first-line treatment between February 2017 and December 2018. Clinical data were collected from electronic medical records. PD-L1 TPS scores were assessed immunohistochemically, using the 22C3 antibody. RESULTS: The median follow-up period was 71.1 months. The median progression-free survival (PFS) was 6.9 months (95 % confidence interval [CI]
4.7-9.1 months), and the 2-, 3-, and 5-year PFS rates were 24.9 %, 19.3 %, and 14.2 %, respectively. The median overall survival (OS) was 19.1 months (95 %CI
13.3-24.9 months). The 2-, 3-, and 5-year OS rates were 42.7 %, 33.9 %, and 24.8 %, respectively. On multivariate analysis, histology (squamous vs. non-squamous cell carcinoma
hazard ratio [HR] 2.23, 95 %CI 1.40-3.89, p = 0.001) and number of metastatic sites (<
3 vs. ≥ 3
HR 4.65 95 %CI 2.51-8.62, p <
0.001) independently affected long-term survival. Immune-related adverse events occurred in 43 cases (45.3 %
20 [21.0 %] Grade ≥ 3). CONCLUSION: The real-world 5-year survival rate of NSCLC cases with PD-L1 ≥ 50 % treated with first-line pembrolizumab was comparable to that in a clinical trial. Histological type and number of metastatic sites influenced long-term and 5-year survival.