Background: MYSTIC, an open-label, Phase 3 trial of first-line D (anti-PD-L1) ± T (anti-CTLA-4) vs platinum CT in mNSCLC, showed an improvement in overall survival (OS) with D vs CT in pts with tumor cell PD-L1 expression ≥25% (TC ≥25% [primary analysis population]; D vs CT, HR 0.76 [97.54% CI 0.56–1.02], p = 0.036; D+T vs CT, HR 0.85 [98.77% CI 0.61–1.17], p = 0.202). Here we summarize PROs from MYSTIC. Methods: Immunotherapy/CT-naïve mNSCLC pts were randomized (1:1:1) to D, D+T, or CT. Symptoms, function, and global health status/quality of life (QoL) were assessed using the EORTC QLQ-C30 v3 questionnaire and its lung cancer module, QLQ-LC13. A change in score from baseline ≥10 points was predefined as clinically meaningful (CM). Mean changes from baseline (over 12 mos) for prespecified symptoms were analyzed using a mixed model for repeated measures (MMRM). Time from randomization to the first CM deterioration (TTD) was analyzed. Results: Among pts with PD-L1 TC ≥25% (n = 488), there were no differences between arms in symptoms, function, or global health status/QoL at baseline. Compliance with completing the questionnaires was ≥60% to wk 120 in the D±T arms, and to wk 40 (C30) and wk 44 (LC13) in the CT arm. MMRM analysis showed significant between-arm differences in changes from baseline in favor of D for fatigue (difference vs CT −9.5) and appetite loss (−11.9; CM), and D+T for fatigue (−11.7; CM). Significantly longer TTD (median, mos) was seen with D and D+T vs CT for appetite loss (12.8 and 5.6 vs 4.5), constipation (14.6 and 9.0 vs 5.5), nausea/vomiting (16.7 and 9.7 vs 4.5), and dyspnea (10.6 and 7.4 vs 5.6); D vs CT for diarrhea (16.3 vs 9.0), insomnia (9.3 vs 6.2), and hemoptysis (not reached vs 10.3); and D+T vs CT for fatigue (5.6 vs 2.0). Significantly longer TTD (median, mos) was also seen with D and D+T vs CT for function (cognitive [9.1 and 6.6 vs 5.2], physical [9.0 and 7.4 vs 4.2], role [D vs CT only; 7.3 vs 3.7], social [12.9 and 5.4 vs 5.2]), and global health status/QoL (5.9 and 6.8 vs 5.5). Conclusions: Pts with PD-L1 TC ≥25% treated with D±T had a reduced symptom burden over time and longer TTD for symptoms, function, and global health status/QoL compared to pts receiving CT. Clinical trial information: NCT02453282