5-year survival outcomes with durvalumab after chemoradiotherapy in unresectable Stage III NSCLC - an update from the PACIFIC trial

8511 Background: In the placebo-controlled Phase III PACIFIC trial of patients with unresectable Stage III NSCLC whose disease had not progressed after platinum-based concurrent chemoradiotherapy (cCRT), durvalumab improved overall survival (OS) (stratified hazard ratio [HR] 0.68; 95% confidence interval [CI] 0.53–0.87; p=0.0025; data cutoff [DCO] Mar 22, 2018) and progression-free survival (PFS) (stratified HR 0.52, 95% CI 0.42–0.65; p<0.0001; DCO Feb 13, 2017) based on the DCOs used for the primary analyses, and the degree of benefit remained consistent in subsequent updates. Durvalumab was associated with a manageable safety profile, and did not detrimentally affect patient-reported outcomes, compared with placebo. These findings established consolidation durvalumab after CRT (the ‘PACIFIC regimen’) as the standard of care in this setting. We report updated, exploratory analyses of OS and PFS, assessed approximately 5 years after the last patient was randomized. Methods: Patients with WHO PS 0/1 (and any tumor PD-L1 status) whose disease did not progress after cCRT (≥2 overlapping cycles) were randomized (2:1) 1–42 days following cCRT (total prescription radiotherapy dose typically 60–66 Gy in 30–33 fractions) to receive 12 months’ durvalumab (10 mg/kg IV every 2 weeks) or placebo, stratified by age (<65 vs ≥65 years), sex, and smoking history (current/former smoker vs never smoked). The primary endpoints were OS and PFS (blinded independent central review; RECIST v1.1) in the intent-to-treat (ITT) population. HRs and 95% CIs were estimated using stratified log-rank tests in the ITT population. Medians and OS/PFS rates at 60 months were estimated with the Kaplan–Meier method. Results: Overall, 709/713 randomized patients received treatment in either the durvalumab (n/N=473/476) or placebo (n/N=236/237) arms. The last patient had completed study treatment in May 2017. As of Jan 11, 2021 (median follow-up duration of 34.2 months in all patients; range, 0.2–74.7 months), updated OS (stratified HR 0.72, 95% CI 0.59–0.89; median 47.5 vs 29.1 months) and PFS (stratified HR 0.55, 95% CI 0.45–0.68; median 16.9 vs 5.6 months) remained consistent with the results from the primary analyses. The 60-month OS rates were 42.9% and 33.4% with durvalumab and placebo, respectively, and 60-month PFS rates were 33.1% and 19.0%, respectively. Updated treatment effect estimates for patient subgroups will be presented. Conclusions: These updated survival analyses, based on 5-year data from PACIFIC, demonstrate robust and sustained OS plus durable PFS benefit with the PACIFIC regimen. An estimated 42.9% of patients randomized to durvalumab remain alive at 5 years and approximately a third remain both alive and free of disease progression. Clinical trial information: NCT02125461.