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The influence of EGFR mutation status and PD-L1 expression in stage III unresectable non-small cell lung cancer treated with chemoradiation and consolidation durvalumab.

e18810 Background: The PACIFIC trial established concurrent chemoradiation followed by one year of consolidation durvalumab as the standard of care for unresectable stage III non-small cell lung cancer (NSCLC). However, the data to support the use of durvalumab in patients with EGFR mutations and low PD-L1 expression is less clear. This study adds to the available evidence by describing the survival outcomes for patients with stage III unresectable NSCLC treated with chemoradiation followed by durvalumab with a focus on their EGFR mutation and PD-L1 status. Methods: This retrospective observational study was conducted at six sites across Sydney, Australia. It included patients diagnosed with unresectable stage III NSCLC treated with chemoradiation and at least one cycle of durvalumab between January 2018 to September 2021. Patients were stratified into EGFR wild-type and mutated tumours and PD-L1 tumour proportional score (TPS) greater than or less than 1%. Survival analyses were supplemented with cox proportional hazards regression models which estimated HRs for PFS in treatment group comparisons. The proportional hazards assumption was confirmed for all cox models. All statistical analysis was done using R version 4.1.1. Results: 146 patients were included in the analysis. The median follow-up from the start of Durvalumab was 15.1 months. The median age was 66 years in the EGFR mutated and 65 years in the EGFR wild-type cohorts. 61% (n = 89) of patients were male. 10% (n = 15) of patients had EGFR mutation. 42% (n = 61) of patients had a PD-L1 TPS of < 1%. PD-L1 expression was similar in both cohorts with 47% (n = 7) of EGFR mutated patients having PD-L1 TPS of < 1% compared with 45% (n = 59) in the wild-type group. The median progression-free survival (PFS) was 7.5 months for EGFR mutated patients versus 33.9 months for EGFR wild- type patients (HR: 2.7; 95% CI: 1.2 – 5.7; p = 0.01). There was no statistically significant difference in either PFS (HR 0.7, 95% CI 0.4 – 1.7, p = 0.43) or OS (HR 0.5, 95% CI 0.4 – 4.7, p = 0.16) for patients with PD-L1 TPS of < 1% compared with PD-L1 TPS of > 1%. Conclusions: Our data adds to the growing evidence that suggests consolidation durvalumab after definitive chemoradiation may not be as efficacious in patients with EGFR-mutated tumours. PD-L1 TPS did not affect survival outcomes.