Background: The European Organisation for Research and Treatment of Cancer (EORTC) 1325-MG/KEYNOTE-054 trial in patients with resected, high-risk stage III melanoma demonstrated improved recurrence-free survival with adjuvant pembrolizumab compared with placebo (hazard ratio 0·57 [98·4% CI 0·43-0·74]; p<0·0001). This study reports the results from the health-related quality-of-life (HRQOL) exploratory endpoint., Methods: This double-blind, randomised, controlled, phase 3 trial was done at 123 academic centres and community hospitals across 23 countries. Patients aged 18 years or older with previously untreated histologically confirmed stage IIIA, IIIB, or IIIC resected cutaneous melanoma, and an Eastern Cooperative Oncology Group performance status score of 1 or 0 were eligible. Patients were randomly assigned (1:1) using a central interactive voice-response system on the basis of a minimisation technique stratified for stage and geographic region to receive intravenously 200 mg pembrolizumab or placebo. Treatment was administered every 3 weeks for 1 year, or until disease recurrence, unacceptable toxicity, or death. The primary endpoint of the trial was recurrence-free survival (reported elsewhere). HRQOL was a prespecified exploratory endpoint, with global health/quality of life (GHQ) over 2 years measured by the EORTC QLQ-C30 as the primary analysis. Analyses were done in the intention-to-treat population. This study is registered with ClinicalTrials.gov, NCT02362594, and EudraCT, 2014-004944-37, and long-term follow-up is ongoing., Findings: Between Aug 26, 2015, and Nov 14, 2016, 1019 patients were assigned to pembrolizumab (n=514) or placebo (n=505). Median follow-up was 15·1 months (IQR 12·8-16·9) at the time of this analysis. HRQOL compliance was greater than 90% at baseline, greater than 70% during the first year, and greater than 60% thereafter for both groups. Because of low absolute compliance numbers at later follow-up, the analysis was truncated to week 84. Baseline GHQ scores were similar between groups (77·55 [SD 18·20] in the pembrolizumab group and 76·54 [17·81] in the placebo group) and remained stable over time. The difference in average GHQ score between the two groups over the 2 years was -2·2 points (95% CI -4·3 to -0·2). The difference in average score during treatment was -1·1 points (95% CI -3·2 to 0·9) and the difference in average score after treatment was -2·2 points (-4·8 to 0·4). These differences are within the 5-point clinical relevance threshold for the QLQ-C30 and are therefore clinically non-significant., Interpretation: Pembrolizumab does not result in a clinically significant decrease in HRQOL compared with placebo when given as adjuvant therapy for patients with resected, high-risk stage III melanoma. These results support the use of adjuvant pembrolizumab in this setting., Funding: Merck Sharp & Dohme., Competing Interests: Declaration of interests AMME reports non-financial support from BMS and Merck & Co during the conduct of the study; personal fees from Biocad, BioInvent, Bristol Myers Squibb (BMS), CatalYm, GSK, IO Biotech, ISA pharmaceuticals, Merck, Novartis, Regeneron, Sellas, SkylineDx, Novartis, and Pfizer, outside the submitted work. AMH reports personal fees from Merck Sharp and Dohme (MSD); and personal fees from Novartis and BMS, outside the submitted work. AJMvdE reports grants and personal fees from BMS; grants from Roche and Idera; and personal fees from MSD, Amgen, Pierre Fabre, and Novartis, outside the submitted work. AM reports personal fees from Lilly Pharma, AstraZeneca Pharmaceuticals, Merck, BMS, and Sanofi-Aventis Group, outside the submitted work AMDG reports advisor or consultant roles from BMS, Pierre Fabre, Sanofi, and MSD, outside the submitted work. ACJvA reports grants and personal fees from Amgen and Merck-Pfizer; and personal fees from BMS, Novartis, MSD-Merck, Sanofi, Sirius Medical, and 4SC, outside the submitted work. CUB reports grants and personal fees from BMS and Novartis; personal fees from Roche, MSD, Pfizer, Lilly, Pierre Fabre, and GenMAb; grants from NanoString and Third Rock Ventures; stock ownership of Unity Cars; and is a cofounder of Immagene, outside the submitted work. CR participated in advisory boards for Roche, Pierre Fabre, Merck, Novartis, Amgen, BMS, Novartis, MSD, Sanofi, Biothera, and Ultimovacs. DS reports personal fees consulting or advisory role, honorarium, speakers bureau, travel, accommodations, and expenses from MSD during the conduct of the study; personal fees and non-financial support from Roche/Genentech, Merck Serono, and Merck; grants, personal fees, non-financial support, consulting or advisory role, honoraria, speakers bureau, travel, accommodations, expenses, and research funding from Novartis and Amgen; grants, personal fees, consulting or advisory role, honoraria, speakers bureau, travel, accommodations, expenses, and research funding from BMS; and personal fees from Immunocore, Incyte, 4SC, Pierre Fabre, Sanofi, Array BioPharma, Pfizer, Philogen, Regeneron, Nektar, and Sandoz, outside the submitted work. GVL reports personal fees from Aduro Biotech, Amgen, Array Biopharma, Boehringer Ingelheim, BMS, Highlight Therapeutics, MSD, Novartis Pharma, QBiotics, Rhegeneron Pharmaceuticals, and SkylineDX, outside the submitted work. NI and CK report personal fees from Merck & Co during the conduct of the study. J-JG reports personal fees from BMS, MSD, Novartis, Roche, Amgen, Pierre Fabre, and Sanofi; and personal fees from Merck and Pfizer, outside the submitted work. JL reports grants and personal fees from BMS, MSD, Pfizer, Novartis, Roche, Immunocore, Achilles therapeutics, and Nektar; personal fees from Eisai, GSK, Kymab, Secarna, AstraZeneca, Boston Biomedical, EUSA Pharma, Ipsen, Imugene, Incyte, iOnctura, Merck Serono, Pierre Fabre, Vitaccess, and Covance; and grants from Aveo and Pharmacyclics, outside the submitted work. LH-A reports personal fees from Merck during the conduct of the study; and personal fees from BMS, Merck, Amgen, Roche, Regeneron, Novartis, Immunocore, Merck-EMD, Corvus, Polynoma, and Genentech, outside the submitted work. MM reports grants from BMS, MSD, and Roche; and advisory board from Pierre Fabre, BMS, and MSD, outside the submitted work. MSC reports personal fees from MSD, BMS, Novartis, Roche, Pierre Fabre, and Sanofi; and personal fees from Merck Serono, Nektar, Eisia, and Ideaya, outside the submitted work. PAA reports grants and personal fees from BMS, Roche-Genentech, and Array; personal fees, advisory or consultant role, and travel support from MSD; personal fees from Novartis, Merck Serono, Pierre Fabre, Incyte, Genmab, NewLink Genetics, Medimmune, AstraZeneca, Syndax, Sun Pharma, Sanofi, Idera, Ultimovacs, Immunocore, 4SC, Alkermes, Italfarmaco, Nektar, and Boehringer Ingelheim, outside the submitted work. PCL reports personal fees and advisory, speaker, and trials roles for BMS, Novartis, Amgen, GSK, and Chugai; and personal fees from Merck, outside the submitted work. PR reports personal fees from MSD, BMS, Novartis, Pierre Fabre, Blueprint Medicines, and Pfizer outside the submitted work. RG reports documentation fees to institution from MSD during the conduct of the study; personal fees and non-financial support from BMS, Roche Pharma, Merck Serono, Pierre Fabre, and Sanofi Regeneron; fees from MSD, Almirall Hermal, SUN Pharma, and 4SC; grants, personal fees, and non-financial support from Amgen and Novartis; grants and personal fees from Pfizer; and grants from Johnson & Johnson, outside the submitted work. RJ reports grants, fees paid to institution for the conduct of studies in melanoma, and grant for Investigator Initiated Trial in metastatic melanoma from BMS during the conduct of the study; grants, per patients fees paid to the institution for the conduct of the study, and grant for Investigator Initiated Trial in metastatic melanoma from Merck; fees paid to the institution for the conduct of studies in melanoma from Roche/Genentech, GSK, AstraZeneca, and Novartis; and grants from Iovance, outside the submitted work; and has acted as a presenter or as a consultant in advisory boards for both BMS and Merck but has not received any monetary compensation for those roles. SD acts as principal investigator in clinical trials promoted by BMS and MSD and has received institutional research grants from BMS and MSD. SP reports grants from Leo Pharma, Almirall, Castle Bioscience, AMLO Bioscience, and Melagenics; personal fees from Amirall, Leo Pharma, Isdin, Sanofi, La Roche Posay, Regeneron, and Pfizer; speaker bureau from La Roche Posay, Roche, Pierre Fabre, BMS, Bioderma, and Sanofi, outside the submitted work. SSa reports personal fees from BMS and MSD outside the submitted work. SSu, MK, CC, and AK report grants from MSD during the conduct of the study. VGA reports personal fees and non-financial support from BMS; personal fees from Merck, MSD, Novartis, Pierre Fabre, Roche, and Nektar; and travel support from Onco-sec, outside the submitted work. All other authors declare no competing interests., (Copyright © 2021 Elsevier Ltd. All rights reserved.)