Durvalumab With or Without Tremelimumab in Combination With Chemotherapy in First-Line Metastatic NSCLC: Five-Year Overall Survival Outcomes from the Phase 3 POSEIDON Trial.

Introduction: The primary analysis (median follow-up 34.9 months across all arms) of the phase 3 POSEIDON study demonstrated a statistically significant overall survival (OS) improvement with first-line tremelimumab plus durvalumab and chemotherapy (T+D+CT) versus CT in patients with EGFR/ALK-wild-type metastatic NSCLC (mNSCLC). D+CT showed a trend for OS improvement versus CT that did not reach statistical significance. This paper reports prespecified OS analyses after longer-term follow-up (median >5 years).

Methods: 1013 patients were randomized (1:1:1) to T+D+CT, D+CT, or CT, stratified by tumor cell (TC) PD-L1 expression (≥50% vs <50%), disease stage (IVA vs IVB), and histology (squamous vs nonsquamous). Serious adverse events were collected during follow-up.

Results: After median follow-up of 63.4 months across all arms, T+D+CT showed sustained OS benefit versus CT (hazard ratio [HR] 0.76, 95% CI: 0.64-0.89; 5-year OS: 15.7% vs 6.8%). OS improvement with D+CT versus CT (HR 0.84, 95% CI: 0.72-1.00; 5-year OS: 13.0%) was consistent with the primary analysis. OS benefit with T+D+CT versus CT remained more pronounced in nonsquamous (HR 0.69, 95% CI: 0.56-0.85) versus squamous (HR 0.85, 95% CI: 0.65-1.10) mNSCLC. OS benefit with T+D+CT versus CT was still evident regardless of PD-L1 expression, including patients with PD-L1 TC <1%, and remained evident in STK11-mutant (nonsquamous), KEAP1-mutant, and KRAS-mutant (nonsquamous) mNSCLC. No new safety signals were identified.

Conclusions: After median follow-up of >5 years, T+D+CT showed durable long-term OS benefit versus CT, supporting its use as first-line treatment in mNSCLC, including in patient subgroups with harder-to-treat disease.