P3.04-13 PD-L1-Gene Expression by Ncounter Correlates with PD-L1 Protein Expression in Advanced Non-Small Cell Lung Cancer (NSCLC)

PD-L1 immunohistochemistry (IHC) staining is a Food and Drug Administration-approved marker to identify patients for immunotherapy treatment in advanced non-small cell lung cancer (NSCLC). However, several antibodies and cut-off criteria have been used and pathological evaluation involves a certain degree of subjectivity. Multiplexed technologies can be of help in this setting and provide an objective measurement of PD-L1 levels. A 7-gene ‘immune signature’ comprising CD4, CD8, PD-1, PD-L1, IFNG, GZMM and FOXP3 was incorporated into our routine clinical practice as part of a customized nCounter panel (NanoString Technologies), which simultaneously screens for gene fusions (ALK, ROS1, RET and NTRK1), MET overexpression and MET exon 14-skipping mutations. Formalin-fixed paraffin embedded (FFPE) samples from advanced NSCLC patients were analyzed with the panel and compared with PD-L1 IHC evaluation on tumor cells, using 22C3 clone antibody. Since 2017, a total of 296 FFPE samples have been analyzed with the nCounter panel. PDL-1 IHC has been performed in 113 FFPE samples, as requested by the oncologist. All samples were evaluable for nCounter and IHC (100%). By IHC, 48/113samples (42.5%) were scored as negative for PD-L1 protein expression, whereas 65/113 (57.5%) were evaluated as positive. Of those, 39 presented moderate (≥1-49%) and 26 (23%) high PD-L1 staining (≥50%). Using an appropriate cut-off value, the levels of PD-L1 mRNA, as determined by the nCounter panel, closely correlated the PD-L1 IHC evaluation, with a 78% of concordance and a 0.554 Cohen’s kappa (confidence interval 95% 0.400- 0.709). PD-L1 mRNA expression closely correlates with PD-L1 protein expression. Clinical validation is warranted to determine if nCounter can be an alternative to IHC for PD-L1 evaluation.