Pts with EGFR/ALK wild-type mNSCLC were randomised 1:1:1 to 1L D (until progression) ± limited-course T (up to 5 doses) + platinum-based CT (up to 4 cycles); or CT (up to 6 cycles)….T+D+CT continued to show OS benefit vs CT (HR 0.75; 95% CI 0.63–0.88) with an estimated 25.0% of pts alive at 3 y vs 13.6% (Table)....Consistent with results at the earlier DCO, OS benefit appeared more pronounced with T+D+CT vs CT in pts with non-squamous (than squamous; data will be presented) histology. A trend for OS benefit with T+D+CT vs CT continued to be observed in non-squamous subgroups with mutations (m) in STK11 (Table)....The results of this exploratory analysis from POSEIDON, after mFU of ∼4 y, demonstrate the durable long-term OS benefit of adding a limited course of T to D and 4 cycles of CT.