Abstract 570: PD-L1 expression in paired non-small cell lung cancer tumor samples

Abstract

Abstract Background There is limited information on changes over time in programmed death ligand 1 (PD-L1) expression in non-small cell lung cancer (NSCLC). Methods PD-L1 expression was assessed in paired tumor samples collected at different time points from the same patient using a prototype immunohistochemistry (IHC) assay with the 22C3 antibody. PD-L1 strong and weak positivity were defined to be traceable to the 1% and 50% cutoffs used in the clinical trial version of the assay. Concordance of PD-L1 expression between samples was analyzed by treating the IHC proportional score as a continuous and categorical variable. Results 90 patients were included (73 from Korea, 17 from Denmark). 75% were male, 37% had squamous cell carcinoma, and 83% had stage I-IIIA disease. 97% of first samples and 53% of second samples were from lung. 89% and 63%, respectively, were surgical samples, with a median interval of 20.9 months (range, 0.1-94.0) between collection dates; 91% of paired samples were collected >3 months apart. A significant correlation of the PD-L1 IHC proportional score was observed for the paired samples (Pearson correlation coefficient, 0.62; P < 0.001). At the second time point, scores were identical in 39% of paired samples, higher in 32%, and lower in 29%. Of note, 12% of PD-L1-negative cases became positive and 20% of PD-L1-positive cases become negative at the second time point. The concordance rate was 56% (95% CI, 46%-67%) when PD-L1 expression was categorized as strong or weak positive or negative (Table). Conclusion Although a significant correlation of the PD-L1 IHC proportional score was observed, this preliminary analysis suggested a discordance rate of 44% between initial and subsequent NSCLC tumor samples when patients were categorized by PD-L1 expression level. Similar results were observed when analyzing paired melanoma samples. This discordance should be considered if PD-L1 expression is used for selection of enrollment in clinical trials. Table. Concordance of PD-L1 Expression in Paired NSCLC Samples (N = 90) Later Time PointPD-L1 ExpressionStrong positive, n (%)Weak positive, n (%)Negative, n (%)Earlier Time PointStrong positive3 (3)3 (3)1 (1)Weak positive7 (8)20 (22)17 (19)Negative011 (12)28 (31) Citation Format: Jhingook Kim, Steffen Filskov Sorensen, Yoon-La Choi, Zhen (Adelle) Wang, Jong-Mu Sun, Hyejoo Choi, Jeanette Baehr Georgsen, Marisa Dolled-Filhart, Kenneth Emancipator, Dianna Y. Wu, Peter Meldgaard, Wei Zhou, Henrik Hager. PD-L1 expression in paired non-small cell lung cancer tumor samples. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 570. doi:10.1158/1538-7445.AM2015-570