High PD-L1 expression among patients with ALK rearranged non–small cell lung cancer and response to first line ALK tyrosine kinase inhibitors.

Abstract

8626 Background: Patients with ALK rearrangements are highly responsive to ALK tyrosine kinase inhibitors (TKIs). Negative prognostic markers to ALK TKIs include TP53 alterations and ALK Variants 3a/b. The prognostic role that PD-L1 expression plays in first line ALK TKI outcomes is less clear. Methods: Retrospective review of patients with metastatic ALK-rearranged NSCLC seen between 2015 - 2022 at the University of Colorado who received first line ALK TKIs was performed. PD-L1 expression was denoted as high (≥50%) or low (< 1% or 1-49%) based on pre-treatment biopsies. Clinicopathologic features, treatment outcomes, and genomic data were collected. Survival outcomes were assessed using Kaplan Meier methods. Multivariate modeling adjusted for brain metastases, TP53 mutations, ALK variant status, and ALK TKI. PD-L1 was overexpressed in EML4-ALK murine cell lines with lentiviruses. In vitro and in vivo response to ALK TKIs were compared to non-infected cell lines. Neutrophils and lymphocytes were quantified on pre-treatment H&E slides. Results: Baseline characteristics of 130 patients are shown. Median PFS was significantly (p < 0.001) longer in the PD-L1 low cohort than the PD-L1 high cohort (21 vs 11 mos, HR 0.44, 95% CI 0.29 – 0.66). There was no difference in OS between the PD-L1 low and PD-L1 high cohort (p = 0.4, 107 vs 91 mos, HR 0.86, 95% CI 0.46 – 1.61). In an alectinib sub-group analysis (n = 89), PD-L1 high expressers had a higher rate of CNS progression (93.0 vs 73.9%, p = 0.022). Forced overexpression of PD-L1 in murine EML4-ALK cell lines exerted no difference to in vitroor in vivo response to alectinib. Pre-treatment biopsies from the PD-L1 high cohort (n = 19) revealed significantly more neutrophils (p = 0.021), but not lymphocytes (p = 0.904). Conclusions: High PD-L1 expression (≥50%) is associated with worse PFS and higher intracranial progression rate among those receiving ALK TKIs. Induced PD-L1 expression in ALK cell lines did not alter in vitro or in vivo ALK TKI sensitivity. Higher neutrophil counts track with high PD-L1 expression (≥50%), suggesting that differences within the immune tumor microenvironment may be relevant. [Table: see text]