EGFR and PDL1: A Match (Not) Made in Heaven-A Real-World Retrospective Analysis of PDL1 Expression in EGFR-Mutated NSCLC.

INTRODUCTION: EGFR (epidermal growth factor receptor) mutant NSCLC (non-small cell lung carcinoma) comprises 35-40% of cases in the Asian NSCLC cohort, compared to 15-20% in the rest of the world. Improved response rates have been observed in terms of PFS (progression-free survival) and ORR (overall response rate) when treated with EGFR TKIs (tyrosine kinase inhibitors). However, resistance eventually ensues regardless of the generation of TKI used. Preclinical studies have reported that PDL1 (programmed death ligand 1) is a downstream target of EGFR and is interposed by IL-6/JAK/STAT3 (interleukin-6/Janus kinase/signal transducer and activator of transcription 3), NF-κB (nuclear factor kappa beta), and p-ERK1/2/p-c-Jun pathways. Hence, it may potentially be repressed by EGFR TKIs. In this retrospective exploratory analysis, we studied whether PDL1 expression affects efficacy of EGFR TKIs and clinical outcome in patients with untreated metastatic EGFR-mutated lung adenocarcinoma. METHODS: This single-center retrospective, exploratory analysis was performed between January 2015 and December 2019. Among 1350 cases of NSCLC, 470 were EGFR mutant, of which PDL1 expression testing was done in 193 patients who were included in this study. RESULTS: Median age was 60 years (range 24-87 years). A total of 116 patients (60.1%) had inframe deletion in exon 19, 52 (26.9%) had L858R, and 25 (13%) had uncommon mutations. The number of patients with PDL1 tumour proportion score (TPS) < 1% was 109 (56.5%); 1-49%, 57 (29.5%); and ≥ 50%, 27 (14%). Comparing clinical characteristics among various PDL1 groups, there were no statistically significant correlations obtained. However, patients with PDL1 > 50% were smokers, and showed a trend for higher disease burden at diagnosis. Median PFS of PDL1 < 1% was 10.14 months, compared to 9.4 months in the PDL1 > 1% group; however, the values did not reach statistical significance. CONCLUSION: The current study was an exploratory retrospective study; however, the results add to the growing body of evidence that PDL1 expression in EGFR-mutated NSCLC does not have any prognostic significance. Also the efficacy of EGFR TKIs is not influenced by variations in PDL1 TPS.