Aims The detection of programmed death-ligand 1 (PD-L1) protein expression on tumour cells by immunohistochemistry (IHC) is a predictor of response to immune checkpoint inhibitors. New immunotherapeutic options are changing the treatment paradigm for patients with advanced non-small cell lung cancer (NSCLC). The aim of this retrospective study was to investigate real-world prevalence of PD-L1 expression in NSCLC and any correlations with clinicopathological features.

Methods We reviewed 425 NSCLC cases at a Sydney metropolitan hospital that had PD-L1 IHC (SP263 clone) expression estimated as part of routine diagnostic assessment during a 30-month period.

Results Overall, 32.2% of cases were negative for PD-L1 expression (<1%), 40.3% demonstrated low expression (1%–49%) and 27.5% exhibited high protein expression (≥50%). High PD-L1 expression rates were more likely in non-lung resection cases and in KRAS mutant NSCLC as opposed to KRAS wildtype, while lower expression rates were more commonly found in EGFR mutant NSCLC compared with EGFR wildtype tumours.

Conclusions Ongoing observation and comparison of PD-L1 expression rates is an important practice for ensuring its validity as a predictive biomarker. The results from our study align with and contribute to the growing field of published real-world PD-L1 prevalence rates in NSCLC.