In Australia, a PD-L1 tumour proportion score (TPS) of ≥50% is required for a patient to be eligible for subsidised pembrolizumab as first-line monotherapy in advanced non-small cell lung cancer (NSCLC), however a TPS of ≥1% can qualify patients for other indications, such as combination chemotherapy/immunotherapy or second-line treatments after platinum-based chemotherapy. PD-L1 TPS assessment is also important for neoadjuvant treatment decisions. A proficiency testing program was established in 2025 with the aim to monitor, improve and harmonise pathologist’s interpretation of the TPS algorithm in non-small cell lung cancer (NSCLC). The assessment was based on clinically relevant PD-L1 thresholds of ≥1% and ≥50%, for treatment decision making pathways. Overall, results showed 91% concordance with 9% of submissions assessed as discordant and potentially affecting patient management. It was recommended that pathologists ensure thorough familiarity with the clinically relevant PD-L1 TPS thresholds (1% and 50%), the established scoring criteria for determining TPS in NSCLC, and the principal interpretive pitfalls, including incorrectly counting immune, necrotic or other benign cells such as macrophages, misinterpreting staining patterns (e.g. cytoplasmic staining only), missing areas of weak intensity, and failing to account for heterogeneous expression or technical artifacts.
Pagliuso et al. (Sun,) studied this question.