ImportanceA key issue for the adjuvant treatment of patients with melanoma is the assessment of the effect of treatment on relapse, survival, and quality of life (QOL).ObjectiveTo compare QOL in patients with resected melanoma at high risk for relapse who were treated with adjuvant pembrolizumab vs standard of care with either ipilimumab or high-dose interferon α 2b (HDI).Design, Setting, and ParticipantsThe S1404 phase 3 randomized clinical trial was conducted by the SWOG Cancer Research Network at 211 community/academic sites in the US, Canada, and Ireland. Patients were enrolled from December 2015 to October 2017. Data analysis for this QOL substudy was completed in March 2022. Overall, 832 patients were evaluable for the primary QOL end point.InterventionsPatients were randomized (1:1) to treatment with adjuvant pembrolizumab vs standard of care with ipilimumab/HDI.Main Outcomes and MeasuresQuality of life was assessed for patients at baseline and cycles 1, 3, 5, 7, and 9 after randomization using the Functional Assessment of Cancer Therapy (FACT) Biological Response Modifiers (FACT-BRM), FACT-General, Functional Assessment of Chronic Illness Therapy–Diarrhea, and European QOL 5-Dimension 3-Level scales. The primary end point was the comparison by arm of cycle 3 FACT-BRM trial outcome index (TOI) scores using linear regression. Linear-mixed models were used to evaluate QOL scores over time. Regression analyses included adjustments for the baseline score, disease stage, and programmed cell death ligand 1 status. A clinically meaningful difference of 5 points was targeted.ResultsAmong 1303 eligible patients (median [range] age, 56.7 [18.3-86.0] years; 524 women [40.2%]; 779 men [59.8%]; 10 Asian [0.8%], 7 Black [0.5%], 44 Hispanic [3.4%], and 1243 White [95.4%] individuals), 1188 (91.1%) had baseline FACT-BRM TOI scores, and 832 were evaluable at cycle 3 (ipilimumab/HDI = 267 [32.1%]; pembrolizumab = 565 [67.9%]). Evaluable patients were predominantly younger than 65 years (623 [74.9%]) and male (779 [58.9%]). Estimates of FACT-BRM TOI cycle 3 compliance did not differ by arm (ipilimumab/HDI, 96.0% vs pembrolizumab, 98.3%; P = .25). The adjusted cycle 3 FACT-BRM TOI score was 9.6 points (95% CI, 7.9-11.3; P < .001) higher (better QOL) for pembrolizumab compared with ipilimumab/HDI, exceeding the prespecified clinically meaningful difference. In linear-mixed models, differences by arm exceeded 5 points in favor of pembrolizumab through cycle 7. In post hoc analyses, FACT-BRM TOI scores favored the pembrolizumab arm compared with the subset of patients receiving ipilimumab (difference, 6.0 points; 95% CI, 4.1-7.8; P < .001) or HDI (difference, 17.0 points; 95% CI, 14.6-19.4; P < .001).Conclusions and RelevanceThis secondary analysis of a phase 3 randomized clinical trial found that adjuvant pembrolizumab improved QOL vs treatment with adjuvant ipilimumab or HDI in patients with high-risk resected melanoma.Trial RegistrationClinicalTrials.gov identifier: NCT02506153