306P Real-world outcomes and determinants of immune-mediated pneumonitis in stage III NSCLC treated with durvalumab after chemoradiotherapy

Results: Among 50 patients with PD-L1 1% (40 Durva, 10 NoDurva), with a PIV cutoff of 332, PFS significantly differed across the four groups (log-rank p=0.00012).Durva_low group had the most favorable PFS, while NoDurva_high group had the poorest outcomes.In multivariable analysis, Durva_low was associated with a significantly lower risk of progression (HR 0.26, 95%CI 0.09-0.78,p=0.016), and NoDurva_high with a higher risk (HR 3.75, 95%CI 1.32-10.69,p=0.013), compared to Durva_high.However, no significant interaction between PIV and treatment group was observed, and PD-L1 was not independently associated with PFS.PIV was not associated with the risk of pneumonitis. Conclusions:PIV is a prognostic biomarker in unresectable stage III NSCLC undergoing CRT, effectively stratifying patients by risk regardless of durvalumab exposure.These findings suggest that PIV may support baseline risk assessment, but do not support a predictive role for PIV in identifying differential benefit from durvalumab.Further validation in a wider cohort is needed.