Background: CAPItello-291 is an ongoing phase 3 trial in which capivasertib-fulvestrant significantly improved progression-free survival versus placebo-fulvestrant in patients with hormone receptor-positive, HER2-negative advanced breast cancer who had relapse or disease progression during or after aromatase inhibitor treatment, in both the overall population and in patients with PIK3CA, AKT1, or PTEN-altered tumours. This study further explored patient-reported health-related quality of life (HRQOL), functioning, symptoms, and symptom tolerability in CAPItello-291., Methods: This phase 3, randomised, double-blind, placebo-controlled trial, which was conducted across 193 hospitals and cancer centres in 19 countries, enrolled women with any menopausal status or men, aged ≥18 years (≥20 years in Japan), with hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer who had relapse or disease progression during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase (CDK) 4 or 6 inhibitor therapy. Patients had an Eastern Cooperative Oncology Group/WHO performance score of 0 or 1 and could have received up to two previous lines of endocrine therapy and up to one previous line of chemotherapy for advanced disease. Patients were randomly assigned (1:1) using block randomisation (stratified according to the presence or absence of liver metastases, previous use of a CDK4/6 inhibitor [yes vs no], and geographical region) to receive oral capivasertib 400 mg (twice daily for 4 days, followed by 3 days off) plus intramuscular fulvestrant 500 mg (every 14 days for the first three injections, then every 28 days) or placebo with matching fulvestrant dosing. The dual primary endpoint of the trial was investigator-assessed progression-free survival assessed both in the overall population and among patients with PIK3CA, AKT1, or PTEN-altered tumours. The EORTC Quality of Life Questionnaire 30-item core module (QLQ-C30) and breast module (QLQ-BR23), Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE), and Patient Global Impression of Treatment Tolerability (PGI-TT) questionnaires were used to assess patient-reported outcomes. Evaluation of EORTC QLQ-C30 and EORTC QLQ-BR23 were secondary endpoints and evaluation of PRO-CTCAE and PGI-TT were pre-defined exploratory endpoints, and these endpoints are the subject of analysis in this Article. Data were collected at baseline and prespecified timepoints. Patient-reported outcomes were analysed in all randomly assigned patients with an evaluable baseline assessment and at least one evaluable post-baseline assessment. Change from baseline was assessed using mixed model with repeated measures for EORTC QLQ-C30 and summarised for QLQ-BR23. Time to deterioration was described using the Kaplan-Meier method. PGI-TT and PRO-CTCAE responses were summarised at each treatment cycle. Patient-reported outcomes were not prospectively powered for statistical comparison. The trial is registered with ClinicalTrials.gov, NCT04305496., Findings: Between June 2, 2020, and Oct 13, 2021, 901 patients were enrolled, of whom 708 patients were randomly assigned to receive capivasertib-fulvestrant (n=355) or placebo-fulvestrant (n=353). The median age of the patients was 59 years (IQR 51-67) in the capivasertib-fulvestrant group and 58 years (IQR 49-66) in the placebo-fulvestrant group. At data cutoff (Aug 15, 2022), the median duration of follow-up for progression-free survival in censored patients was 13·0 months (IQR 9·1-16·7) for capivasertib-fulvestrant and 12·7 months (IQR 2·0-16·4) for placebo-fulvestrant in the overall population. EORTC QLQ-C30 global health status/quality of life (GHS/QOL) scores were maintained from baseline and were similar between treatment groups throughout the study period (difference in mean change from baseline of -2·5 [95% CI -4·5 to -0·6] with capivasertib-fulvestrant vs -5·6 [-7·9 to -3·4] with placebo-fulvestrant; treatment difference 3·1 [95% CI 0·2 to 6·0]). Median time to deterioration in EORTC QLQ-C30 GHS/QOL was 24·9 months (95% CI 13·8 to not reached) in the capivasertib-fulvestrant group and 12·0 months (10·2 to 15·7) in the placebo-fulvestrant group (hazard ratio [HR] 0·70, 95% CI 0·53 to 0·92). Time to deterioration HRs for all EORTC QLQ-C30 and QLQ-BR23 subscale scores showed little difference between the treatment groups, except for diarrhoea, which was worse in the capivasertib-fulvestrant group than in the placebo-fulvestrant group (HR 2·75, 95% CI 2·01-3·81). In PRO-CTCAE symptom assessment, the proportion of patients reporting loose and watery stools "frequently" or "almost constantly" was 29% higher at cycle 1, day 15 in the capivasertib-fulvestrant group than in the placebo-fulvestrant group, decreasing at subsequent cycles. Other PRO-CTCAE-reported symptoms (rash, mouth or throat sores, itchy skin, and numbness or tingling in hands or feet) were absent or mild in most patients in both groups throughout treatment. According to the PGI-TT, most patients in both groups reported "not at all" or "a little bit" of bother from treatment side-effects., Interpretation: Patient-reported outcomes from CAPItello-291 demonstrated that capivasertib-fulvestrant delayed time to deterioration of GHS/QOL and maintained other dimensions of HRQOL (except symptoms of diarrhoea) similarly to fulvestrant. With the clinical efficacy and manageable safety profile, these exploratory results further support the positive benefit-risk profile of capivasertib-fulvestrant in this population., Funding: AstraZeneca., Competing Interests: Declaration of interests MOl has received honoraria from Eisai, Gilead Sciences, Libbs, Eli Lilly, Novartis, Pfizer, Roche, Seagen, AstraZeneca Taiwan, and Merck Sharp & Dohme; has received research funding from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Roche, Seagen, Zenith Epigenetics, Gilead Sciences, Ayala Pharmaceuticals, and Genentech; has received travel grants from Eisai and Gilead Sciences; has served as a consultant for AstraZeneca, Daiichi Sankyo, Gilead Sciences, ITeos Therapeutics, Eli Lilly, Merck Sharp & Dohme, Relay Therapeutics, Roche, Seagen, and Pierre Fabre; and serves as the head on the board of directors for the SOLTI Breast Cancer Research Group. HSR has served as a consultant or advisor for Napo Pharmaceuticals, Puma Biotechnology, Mylan, Eisai, and Daiichi Sankyo, and has received research funding from OBI Pharma, Pfizer, Novartis, Eli Lilly, Merck Sharp & Dohme, Daiichi Sankyo, AstraZeneca, Gilead Sciences, Astellas Pharma, Taiho Oncology, Veru, GlaxoSmithKline, Genentech/Roche, and Stemline Therapeutics. SJH has received institutional grants from Eli Lilly; has served as a consultant for Pfizer; has received payments to their institution per patient from AstraZeneca (study sponsor); has participated on a Data Safety Monitoring Board or Advisory Board for Eli Lilly; has received honoraria from Eli Lilly, Pfizer, Novartis, and AstraZeneca; and has received support for attending meetings and travel from Novartis. FD has received honoraria from Eli Lilly, Gilead Sciences, and AstraZeneca and has received travel grants from Daiichi Sankyo, Novartis, Gilead Sciences, and Pfizer. JC has served as a consultant or advisor for Celgene, Cellestia Biotech, AstraZeneca, Roche, Seagen, Daiichi Sankyo, ERYTECH Pharma, Polyphor, Athenex Oncology, Eli Lilly, SERVIER, Merck Sharp & Dohme, GlaxoSmithKline, Leuko, Clovis Oncology, Bioasis, Boehringer Ingelheim, Ellipses Pharma, HiberCell, Bioinvent, GEMoaB Monoclonals, Gilead Sciences, Menarini, Zymeworks, Reveal Genomics, Expres2ion Biotechnologies, Jazz Pharmaceuticals, AbbVie, Bridgebio, and BioNTech; has received travel grants from Roche, Pfizer, Eisai, Novartis, Daiichi Sankyo, Gilead Sciences, AstraZeneca, Merck Sharp & Dohme, and Stemline Therapeutics; holds stock in Leuko and MAJ3 Capital; holds two patents, WO 2014/199294 A and US 2019/ 0338368 A1; has received honoraria from Novartis, Eisai, Celgene, Pfizer, Roche, Samsung, Eli Lilly, Merck Sharp & Dohme, Daiichi Sankyo, AstraZeneca, Gilead Sciences, and Stemline Therapeutics; and has received research funding from ARIAD Pharmaceuticals, AstraZeneca, Baxalta, Bayer, Eisai, Guardant Health, Merck Sharp & Dohme, Pfizer, Puma Biotechnology, Queen Mary University of London, Roche, and Piqur. HLG has served as a consultant or advisor for AstraZeneca; has received research funding from Merck Sharp & Dohme; and has served on speakers’ bureaus for Roche, AstraZeneca, Bristol Myers Squibb, Merck Sharp & Dohme, Technofarma, and Novartis. MT has served on advisory boards for Athenex Oncology, Bertis, Bristol Myers Squibb, Daiichi Sankyo, Eli Lilly, Kansai Medical Net, and Terumo; has received compensation as an invited speaker from AstraZeneca, Bertis, Bristol Myers Squibb, Chugai, Devicore Medical Japan, Eisai, Eli Lilly, Exact Science, Kyowa-Kirin, Merck Sharp & Dohme, Nippon-Kayaku, Novartis, Pfizer, Shimadzu, Sysmex, Taiho, Takeda, and Yakult; has received research funding from AFI Technology, Astellas, AstraZeneca, Chugai, Daiichi Sankyo, Eisai, Eli Lilly, GL Science, Kansai Medical Net, Luxonus, Pfizer, Sanwa Shurui, Shimadzu, Takeda, The Japan Breast Cancer Research Group association, The Kyoto Breast Cancer Research Network association, and Yakult; has served on steering committees for AstraZeneca, Chugai, and Daiichi Sankyo; and serves as a member of the board of directors for the Organisation for Oncology and Translational Research, The Japan Breast Cancer Research Group association, The Japanese Onco-Cardiology Society, The Kyoto Breast Cancer Research Network association, and The Japanese Breast Cancer Society. KJ has served on advisory boards for Novartis, Pfizer, AstraZeneca, Jounce Therapeutics, Synthon, Intellisphere, Bristol Myers Squibb, Genentech, AbbVie, Eli Lilly, BluePrint Medicines, Seagen, Daiichi Sankyo, Biotheranostics, Sun Pharma Advanced Research Company, Taiho Oncology, Sanofi, Gilead Sciences, and Scorpion Therapeutics; has received research funding from Novartis, Genentech, Debiopharm Group, ADC Therapeutics, Pfizer, Novita Pharmaceuticals, Clovis Oncology, Eli Lilly, Zymeworks, Immunomedics, Puma Biotechnology, VelosBio/Merck, AstraZeneca, Context Therapeutics, Scorpion Therapeutics, and Blueprint Medicines; and has received travel grants from Taiho Pharmaceutical, Jounce Therapeutics, Pfizer, AstraZeneca, Intellisphere, Eli Lilly, Gilead Sciences, and Genentech/Roche. SL has served as a consult or on advisory boards for AbbVie, Amgen, AstraZeneca, Bristol Myers Squibb, Celgene, Daiichi Sankyo, EirGenix, Gilead Sciences, GlaxoSmithKline, Eli Lilly, Merck, Novartis, Olema, Pfizer, Pierre Fabre, Relay Therapeutics, Roche, Sanofi, Seagen, and AGO (German Gynecological Oncology Group) Kommission Mamma; has served as an invited speaker at AstraZeneca, DSI, Gilead Sciences, Novartis, Pfizer, Roche, Seagen, Stemline-Menarini, and Medscape; is a full or part-time employee at GBG Forschungs GmbH; has received licensing or royalties from VMscope GmbH, and research funding from AbbVie, AstraZeneca, Celgene, Daiichi Sankyo, Greenwich Life Sciences, Immunomedics/Gilead Sciences, Molecular Health, Novartis, Pfizer, and Roche; and has served as a principal investigator at PI Aphinity. YHP has received research funding from MSD, Pfizer, Roche, Novartis, AstraZeneca, Gencurix, and Genome Insight; has received honoraria from AstraZeneca, Pfizer, Eli Lilly, MSD, Roche, Daiichi Sankyo, Novartis, and Gilead Sciences; has received consulting fees from AstraZeneca, Pfizer, Eli Lilly, Gilead Sciences, MSD, Eisai, Roche, Daiichi Sankyo, Menarini, Everest, and Novartis; has received travel grants from Gilead Sciences, Pfizer, and AstraZeneca; has served on advisory boards for AstraZeneca, Pfizer, Roche, Menarini, Novartis, Daiichi Sankyo; and has received equipment, materials, drugs, medical writing, gifts, or other services from Dong-A ST, Sanofi, Roche, and Pfizer. JHS has received research funding from MSD, Roche, Novartis, Eli Lilly, Pfizer, Daiichi Sankyo, AstraZeneca, GlaxoSmithKline, Sanofi, Boehringer Ingelheim, Seagen, Qurient, Dragonfly Therapeutics, Eikon Therapeutics, Gilead Sciences, Celcuity, Bristol Myers Squibb, HLB Pharmaceutical, Sermonix Pharmaceuticals, Olema Oncology, Hanmi, Ildong Pharmaceutical, and Samyang Holdings. ET has received honoraria from Eli Lilly, Daiichi Sankyo, AstraZeneca, and Chugai. NCT has served on the advisory board for AstraZeneca, Eli Lilly, Novartis, Pfizer, Roche/Genentech, GlaxoSmithKline, Repare Therapeutics, Relay Therapeutics, Gilead Sciences, Inivata, Guardant Health, and Exact Sciences and received research funding from AstraZeneca, Pfizer, Roche/Genentech, MSD, Invitae, Inivata, Personalis, and Natera. CD’C, HA, MF, and IW are employees of AstraZeneca, and may hold AstraZeneca stocks or shares. All other authors declare no competing interests., (Copyright © 2024 Elsevier Ltd. 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