Background: PERLA (NCT04581824) is a global, randomized, Phase II, double-blind study assessing the efficacy and safety of chemotherapy (CT) combined with programmed death 1 (PD-1) inhibitors dostarlimab (dostCT) and pembrolizumab (pembCT) as first-line (1L) treatment (tx) for patients (pts) with metastatic non-oncogene-driven, non-squamous, NSCLC. DostCT had similar efficacy and safety to pembCT [1]. Exploratory analyses of patient-reported outcomes (PROs) from PERLA have been conducted. Methods: In PERLA, pts with ECOG status 0–1 were randomized 1:1 to receive ≤35 cycles (C) of dostCT or pembCT Q3W (CT was ≤35 cycles [C] of 500 mg/m² pemetrexed every 3 weeks [Q3W] and ≤4C of cisplatin or carboplatin). PROs were collected at baseline (BL), Q3W until C4, Q9W until C16, Q12W until end of tx and at 30-day safety follow-up. Change from BL in EORTC QLQ-C30 & QLQ-LC13 were analyzed using a longitudinal mixed model, with a ≥10-point change from BL considered clinically meaningful; scores were categorized as improved, stable, or worsened. Time to deterioration (TTD) in QLQ-C30 and selected QLQ-LC13 symptoms were estimated using Kaplan–Meier methods. Results: Analysis populations for dostCT/pembCT included 102/99 pts for QLQ-C30 and 96/90 pts for QLQ-LC13. Completion rates for QLQ-C30 and QLQ-LC13 were >80% up to C4 in both tx arms, decreasing after C7. At C13, 55.0% [n=33/60] and 54.2% [n=32/59] of dostCT pts, and 37.1% [n=23/62] and 35.7% [n=20/56] of pembCT pts completed QLQ-C30 and QLQ-LC13, respectively. Overall, least squares (LS) mean QLQ-C30 and QLQ-LC13 scores remained stable up to C13. Relative to BL, average pt functioning (e.g., physical, role) and cancer symptoms (e.g., pain, cough, dyspnea) were stable through C13 (~1 yr on tx); no clinically meaningful difference in LS mean QLQ-C30 or QLQ-LC13 scores were observed between tx arms. Across most QLQ-C30 and QLQ-LC13 subscales, >60% pts in both tx arms had stable or improved responses up to C13. At C13, meaningful improvements in chest pain and dyspnea were reported in a higher % of dostCT pts (34.4% [n=11/32] and 40.6% [n=13/32], respectively) than pembCT pts (10.0% [n=2/20] and 25.0% [n=5/20], respectively). TTD for QLQ-C30 and QLQ-LC13 subscales were comparable between tx arms, except for longer median TTD in dyspnea in dostCT pts (N=96) than pembCT pts (N=90) (4.24 vs 1.54 months; HR 0.64 [95% CI: 0.44–0.93]). Conclusions: HRQoL was similar and stable through C13 in both tx arms. These results supplement efficacy and safety data reported in PERLA and support further investigation of dostarlimab as an appropriate PD-1 inhibitor for use in combination with standard of care and novel therapies in metastatic NSCLC. References: 1. Peters, S et al. IOTECH 2022;16(S1):100162 Funding:GSK (213403). Editorial support provided by Fishawack Health, funded by GSK. Clinical trial information: NCT04581824.