Background: In KEYNOTE-119 (ClinicalTrials.gov, NCT02555657), overall survival (primary end-point) was similar between pembrolizumab and chemotherapy in patients with previously treated metastatic triple-negative breast cancer (TNBC), although the pembrolizumab treatment effect increased with tumour PD-L1 expression. We report results of prespecified health-related quality of life (HRQoL) analyses from KEYNOTE-119., Methods: Eligible patients were randomised 1:1 to pembrolizumab 200 mg Q3W intravenously for up to 35 cycles or treatment of physician's choice per local/country guidelines. Prespecified exploratory end-points were the change from baseline in HRQoL (EORTC QLQ-C30, QLQ-BR23) and to characterise utilities (EQ-5D-3L). Time to deterioration (TTD) was the time from start of treatment to first onset of a ≥10-point worsening from baseline., Results: HRQoL analyses included 187 patients with tumour PD-L1 combined positive score (CPS) ≥10. Changes from baseline at 6 weeks (primary analysis time point) were directionally better with pembrolizumab versus chemotherapy for QLQ-C30 GHS/QoL (between-group difference in least-squares mean scores of 4.21 [95% CI, -1.38 to 9.80]), QLQ-C30 functional scales (physical, role, cognitive, social), QLQ-C30 symptom scales/items (fatigue, nausea/vomiting, dyspnoea, appetite loss), and QLQ-BR23 symptom scales/items (systemic therapy side-effects, upset by hair loss). Median TTD was directionally longer for pembrolizumab versus chemotherapy for QLQ-C30 QHS/QoL (4.3 versus 1.7 months), QLQ-C30 nausea/vomiting (7.7 versus 4.8 months), and QLQ-BR23 systemic therapy side-effects (6.1 versus 3.4 months). Minimal treatment differences were observed for other HRQoL end-points., Conclusions: HRQoL results were consistent with clinical outcomes and appeared to be driven by results for patients with tumour PD-L1 CPS ≥10., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Peter Schmid: Consultant/Honoraria: AstraZeneca, Bayer, Boehringer Ingelheim, Celgene, Eisai, Merck Sharp, and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, Pfizer, Puma, and Roche; grant funding to institution: Astellas, AstraZeneca, Genentech, Medivation, Novartis, Oncogenex, and Roche. Oleg Lipatov: Nothing to disclose. Seock-Ah Im: consulting/advisory role: AstraZeneca, Novartis, Roche/Genentech, Pfizer, Amgen, Hanmi, Lilly, GlaxoSmithKline, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Daiichi Sankyo, Idience Co. Ltd., and Bertis; research funding to institution: AstraZeneca, Pfizer, Roche/Genentech, Daewoong Pharmaceutical, Eisai Korea, and Boryung Pharm. Anthony Goncalves: Nonfinancial support/consultant (compensated to hospital): AstraZeneca, Novartis, Astellas, Pfizer, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Lilly, Mylan, Parexel, and Roche. Eva Muñoz-Couselo: Nothing to disclose. Keun Seok Lee: Consultant: Lilly, Novartis, Pfizer, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Bixink, Everest Medicine, Daiichi Sankyo, and Roche; drug supplies: Dong-A Pharm. Kenji Tamura: Nothing to disclose. Laura Testa: Funding for the current trial conduct, provision of study materials, medical writing, and article processing charges: Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; research grant: Novartis; payment or honoraria for medical education: Lilly, Novartis, Pfizer, AstraZeneca, Daiichi-Sankyo, and Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; support for attending meetings and/or travel: Roche, Gilead, and AstraZeneca; Data Safety Monitoring/Advisory board: AstraZeneca, Lilly, Novartis, Merck Sharp, and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Daichi-Sankyo, and Pfizer; steering committee for trials: AstraZeneca and Lilly. Isabell Witzel: Research funding to institution: Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; personal fees: Daiichi Sankyo, Merck Sharp, and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, Pfizer, and Roche. Shoichiro Ohtani: Lecture fees: AstraZeneca, Chugai, Lilly, and Pfizer. Nicholas Turner: Advisory board honoraria: AstraZeneca, Lilly, Pfizer, Roche/Genentech, Novartis, GlaxoSmithKline, Repare Therapeutics, Relay Therapeutics, Zentalis, Gilead, Inivata, Guardant, and Exact Sciences; research funding: AstraZeneca, Pfizer, Roche/Genentech, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Guardant Health, Invitae, Inivata, Personalis, and Natera. Stefania Zambelli: Nothing to disclose. Nadia Harbeck: Consulting/Lecture fees: AstraZeneca, Daiichi Sankyo, Lilly, Merck Sharp, and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, Pfizer, Pierre Fabre, Roche, Sandoz, and Seattle Genetics. Fabrice Andre: Research grants to institution: AstraZeneca, Daiichi Sankyo, Lilly, Novartis, Pfizer, and Roche; Advisory board or speaker (compensation to institution): AstraZeneca, Daiichi Sankyo, Roche, Lilly, Pfizer, Owkin, Novartis, and Guardant Health; and personal fees (advisory board): Lilly. Rebecca Dent: Advisory board: AstraZeneca, Eisai, Eli Lilly and Company, Genentech, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, and Pfizer; Consultant: Genentech; Travel: Genentech, Merck Sharp and Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and Pfizer. Jaime A. Mejia: employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; owns stock in Merck & Co., Inc., Rahway, NJ, USA. Xuan Zhou: Employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; owns stock in Merck & Co., Inc., Rahway, NJ, USA. Amin Haiderali: employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; owns stock in Merck & Co., Inc., Rahway, NJ, USA. Allison Martin Nguyen: Employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA; owns stock in Merck & Co., Inc., Rahway, NJ, USA. Javier Cortes: Consulting fees: AstraZeneca, Athenex, Bioasis, BioInvent, Boehringer Ingelheim, Celgene, Cellestia, Clovis Oncology, Daiichi Sankyo, Ellipses, Erytech, Gemoab, Gilead, GSK, Hibercell, Leuko, Lilly, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Polyphor, Roche, and Seattle Genetics; fees for non-CME services received directly from commercial interest or their agents (e.g., speakers' bureaus): Celgene, Daiichi Sankyo, Eisai, Lilly, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Novartis, Pfizer, Roche, and Samsung Bioepis; contracted research: Ariad Pharmaceuticals, AstraZeneca, Baxalta GMBH/Servier Affaires, Bayer Healthcare, Eisai, F. Hoffman-La Roche, Guardant Health, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, Pfizer, Piqur Therapeutics, Puma, Queen Mary University of London, and Roche; Ownership interest (stock, stock options, or other ownership interest excluding diversified mutual funds): MedSIR; Travel/Accommodation: Daiichi Sankyo, Eisai, Novartis, Pfizer, and Roche; Patent: HER2 as a predictor of response to dual HER2 blockade in the absence of cytotoxic therapy. Eric P. Winer: Advisory board member: LEAP; Consultant: G1 Therapeutics, Garrick Therapeutics, Genomic Health, GlaxoSmithKline, Jounce, Lilly, Novartis, Roche Genentech, Seattle Genetics, and Syros., (Copyright © 2023 Elsevier Ltd. All rights reserved.)