Correlation between PD-L1 expression (clones 28-8 and SP263) and histopathology in lung adenocarcinoma

Lung cancer is the leading cause of cancer-related death worldwide. Recent advances in the management of non-small cell carcinoma are focused on the discovery of targeted therapies and novel immunotherapy strategies for patients with advanced disease. Treatment with anti PD-(L)1 immune checkpoint inhibitors requires the development of predictive biomarkers to select those patients that can most benefit from these therapies. Several immunohistochemical biomarkers have been developed in different technological platforms. However, the most useful and accessible for the daily clinical practice need to be selected. The objective of this study was to compare PD-L1 expression by automated immunohistochemistry in lung adenocarcinoma (ADC) FFPE samples with clones 28-8 and SP263 performed with the BenchMark GX automated staining instrument. To further determine interobserver agreement between two pathologists, and to correlate the results with histologic and pathology variables. FFPE tissue from 40 samples obtained from patients with lung ADC were reviewed retrospectively. Among all studied specimens, 53% of samples presented <1% of positive tumor cells with the 28-8 clone and 50% had <1% of PD-L1 expression in tumor cells with the SP263 clone; PD-L1 expression between ≥1 and <5% was observed in 18% and 24%; ≥5 and <50% PD-L1 expression in 18% and 21%; and ≥50% PD-L1 expression in 11% and 5% of samples, respectively. Similar results between antibodies were observed in 84% of cases for each of the four PD-L1 cutoff groups (Pearson's score 0.90, p < 0.00001). The interobserver degree of agreement calculated with Kappa was 0.75 (95%CI: 0.57–0.93), z = 7.08; p < 0.001. Lepidic, acinar and mucinous patterns had predominantly <1% PD-L1 expression, and the solid pattern subtype had high levels of PD-L1 staining using both clones. PD-L1 expression in less than 1% of tumor cells was similar in stages I/II compared to III/IV. No significant differences were observed in PD-L1 staining and quantification pattern between IHC antibodies 28-8 and SP263.