Intra- and Interobserver Reproducibility Assessment of PD-L1 Biomarker in Non–Small Cell Lung Cancer

Abstract

Reliable and reproducible methods for identifying PD-L1 expression on tumor cells are necessary to identify responders to anti-PD-1 therapy. We tested the reproducibility of the assessment of PD-L1 expression in non-small cell lung cancer (NSCLC) tissue samples by pathologists. NSCLC samples were stained with PD-L1 22C3 pharmDx kit using the Dako Autostainer Link 48 Platform. Two sample sets of 60 samples each were designed to assess inter- and intraobserver reproducibility considering two cut points for positivity: 1% or 50% of PD-L1 stained tumor cells. A randomization process was used to obtain equal distribution of PD-L1 positive and negative samples within each sample set. Ten pathologists were randomly assigned to two subgroups. Subgroup 1 analyzed all samples on two consecutive days. Subgroup 2 performed the same assessments, except they received a 1-hour training session prior to the second assessment. For intraobserver reproducibility, the overall percent agreement (OPA) was 89.7% [95% confidence interval (CI), 85.7-92.6] for the 1% cut point and 91.3% (95% CI, 87.6-94.0) for the 50% cut point. For interobserver reproducibility, OPA was 84.2% (95% CI, 82.8-85.5) for the 1% cut point and 81.9% (95% CI, 80.4-83.3) for the 50% cut point, and Cohen's κ coefficients were 0.68 (95% CI, 0.65-0.71) and 0.58 (95% CI, 0.55-0.62), respectively. The training was found to have no or very little impact on intra- or interobserver reproducibility. Pathologists reported good reproducibility at both 1% and 50% cut points. More adapted training could potentially increase reliability, in particular for samples with PD-L1 proportion, scores around 50%. .

Reproducibility of PD-L1 assessment in non-small cell lung cancer—know your limits but never stop trying to exceed them

“…Moreover, the authors report a lower prevalence of PD-L1 positivity (10.3% with PD-L1 TPS ≥50%) compared to previously published data (i.e., approximately 23%) (7). The nature of the samples used in the study, including the use of tissue micro-arrays, early stage rather than late stage tumors, a high proportion of well differentiated tumors and potentially the use of archived samples, could explain this difference (12). This is the first study to report on intra-observer reproducibility.…”

“…Subgroup two performed the same assessments except they received a 1-hour training session prior to the second assessment. This study reports results on the reproducibility of the pathologists' assessments with a large number of both observers and samples, ensuring good reliability in terms of precision of the calculated values and robustness of the study results, which are more likely to reflect real-life practice (12).…”

“…Although tremendous efforts have been made to adjust several methodological and biological aspects that may influence the outcome of the PD-L1 assay (i.e., tumor heterogeneity, pre-analytical parameters, assay harmonization, validation; IASLC Atlas of PD-L1 Testing in Lung Cancer), the post-analytical phase, and in particular the interpretation and scoring of PD-L1 expression, may hamper the robustness of a PD-L1 assay for surgical pathologists in their daily practice (12,13).…”

“…There is limited data assessing the reproducibility of interpretation and scoring of PD-L1 expression in NSCLC tissue samples and most studies only involve a few pathologists or small numbers of tumors, making it easy to achieve concordance (12)(13)(14)(15)(16). Whereas some studies assessed PD-L1 interpretation reproducibility on resection specimens, only a few studies used smaller sized specimens such as tissue micro-arrays, but none on bronchial or transthoracic biopsies (12)(13)(14)(15)(16).…”

“…Cooper et al, assessed the intra-and inter-observer reproducibility as well as the impact of training of the pathologists in scoring of PD-L1 in NSCLC using the FDA-approved companion diagnostic PD-L1 22C3 pharmDx assay (Agilent) considering two cut points for positivity, 1% and 50% PD-L1 stained tumor cells (12). A representative sample, in terms of demography (i.e., age, type of practice and experience, median 15 years), of ten surgical pathologists were randomly and equally assigned to two subgroups to evaluate a total of 108 NSCLC samples.…”