Background: Alemtuzumab is approved in the European Union for treating highly active relapsing-remitting multiple sclerosis (RRMS). Patient-reported outcomes measure the treatment impact on quality of life (QoL), including fatigue, a common symptom in multiple sclerosis (MS). Chronic diseases like MS also affect the patient's caregiver. Thus, understanding the impact on both patients and caregivers is essential for a comprehensive view of MS treatment outcomes., Methods: This multi-center prospective, observational study assessed RRMS patients undergoing alemtuzumab treatment, and their caregivers across three European countries (Denmark, Norway, and Italy). The study visits were conducted at baseline, and at Months 3, 6, 12, 18, 24, and 36 (± 1 month). The primary endpoint assessed the effect of alemtuzumab on MS-related fatigue (Fatigue Scale for Motor and Cognitive Functions [FSMC] score). Secondary endpoints included changes in cognition (Symbol Digit Modalities Test [SDMT]), depression (Beck Depression Inventory-Version II [BDI-II]), QoL (29-item Multiple Sclerosis Impact Scale [MSIS-29]), treatment satisfaction (Treatment Satisfaction Questionnaire for Medication [TSQM]), working capacity/daily life activity (Health-Related Productivity Questionnaire [HRPQ]), and clinical evaluation (number of relapses, improvement in Expanded Disability Status Scale [EDSS] score, and need for re-treatment with alemtuzumab/any other treatment). Exploratory endpoints included caregiver perception of patient's QoL, caregiver QoL, and caregiver burden. The sample size (N = 80) was determined based on the 2-sided t-test at 5 % significance level. Data were analyzed descriptively. Safety was also evaluated., Results: Of 87 enrolled patients, 72.4 % (n = 63) completed all follow-ups. Significant improvement was observed in fatigue (p < 0.01), with a median (min, max) FSMC score change of -7.3 (-56.0, 34.0) units at the end-of-study (EOS), and clinically relevant improvement (≥ 9 units) noted in approximately 12.5 months. SDMT (3-5 units, p<0.05), BDI-II (median score of 9.5, i.e., no depression, p<0.01), and MSIS-29 (median change in physical and psychological impact scores -9.2, p < 0.01 and -14.8, p < 0.001, respectively) improved significantly from baseline to EOS. Global treatment satisfaction (p < 0.001), effectiveness (p < 0.05), and side effects (p < 0.05) significant improved exept at EOS, whereas treatment convenience remained same throughout the study. The percentage of patients with at least one relapse was similar each year of the study (10.8-13.2 %). A statistically significant improvement (p < 0.05) in EDSS was reported over time. At EOS, 4.5 % patients needed retreatment with alemtuzumab. Caregivers also reported improvement in patients' QoL over time, but the median change from baseline (physical and psychological impact scores:10.0 and -14.8, respectively) was not statistically significant (p > 0.05). Caregivers reported similar QoL and caregiver burden at baseline and EOS, apart from an increase in emotional QoL. Headache (51.2 %), pyrexia (44.2 %), and rash (34.9 %) were the most common adverse events (AEs). Majority of the AEs were either mild or moderate, apart from 25 severe AEs. Three patients discontinued prematurely, of which one patient died of sepsis related to treatment., Conclusion: This real-world study showed beneficial impact of alemtuzumab on fatigue, cognition, depression, QoL, and treatment satisfaction. Improvement in patient disability, and caregiver-reported outcomes indicated enhanced patients' QoL., Competing Interests: Declaration of competing interest Jette Lautrup Frederiksen: Served on scientific advisory boards for and received funding for travel related to these activities as well as honoraria from Biogen Idec, Merck Serono, Sanofi-Aventis, Teva, Novartis, and Almirall. Received speaker honoraria from Biogen Idec, Teva, and Novartis. Luca Massacesi: Received educational grants and/or research funds from Biogen, Merck-Serono, Genzyme, and Roche and honoraria or consultation fees from Biogen, Roche, Merck-Serono, Sanofi, Viatris, Horizon, Alexion, and Novartis. Helle Hvilsted Nielsen: Received research support, travel grants, and/or teaching honoraria from Biogen Inc., Merck Serono, Novartis, Sanofi, Teva, and Roche. Augusto Rini: Received a grant for the organization of a scientific congress or speaker honoraria from Biogen Idec, Sanofi, Merck Serono, Bristol, and Roche. Eleonora Baldi: Received a grant for the organization of a scientific congress from Biogen Idec and also received travel or speaker honoraria from Biogen Idec, Sanofi, Merck Serono, Novartis, and Roche. Massimiliano Mirabella: Reported scientific advisory board membership with Bayer Schering, Biogen, Sanofi, Merck, Novartis, and Roche; received consulting and/or speaking fees and research support or travel grants from Almirall, Alexion, Bayer Schering, Bristol-Myers-Squibb, Biogen, Janssen, Sanofi, Merck, Novartis, Roche, and Viatris; reported to be a principal investigator in clinical trials conducted by Biogen, Merck, Novartis, Roche, and Sanofi. Falzone Francesca Maria Antonella: Received travel or speaker honoraria and grants to attend scientific congresses from Biogen, Sanofi, Merck Serono, and Teva. Received a grant for the organization of a scientific congress from Biogen. Giacomo Lus: Received speaker, travel, and advisory board membership honoraria from Almirall, Alexion, Bayer, Biogen, Novartis, Sanofi, Merck, Bristol-Myers-Squibb, and Horizon Therapeutics. Damiano Paolicelli: Received speaker honoraria from Novartis, Sanofi, Biogen Idec, Merck-Serono, Roche, BMS, and Almirall. Matthias Kant: Has nothing to disclose. Giuseppe Salemi: Received grants to attend scientific congresses or speaker honoraria from Biogen, Merck-Serono, Novartis, Roche, Sanofi, and Teva. Umberto Aguglia: Received grants to attend scientific congresses or speaker honoraria from Biogen, Merck-Serono, Novartis, Roche, Sanofi, and Teva. Cristoforo Comi: Received grants to attend scientific congresses or speaker honoraria from Merck-Serono, Novartis, Roche, Sanofi, and Almirall. Milena De Riz: Received grants to attend scientific congresses or speaker honoraria from Merck-Serono, Novartis, Roche, Sanofi, Biogen, Teva, Almirall, Bristol-Myers-Squibb, and Horizon Therapeutics. Valeria Barcella: Received grants to attend scientific congresses or speaker honoraria from Biogen, Merck-Serono, Novartis, Roche, Sanofi, and Teva. Heidi Ø. Flemmen: Received unrestricted research grants from Biogen and Novartis and advisory board and/or speaker honoraria from Sanofi, Merck, and Biogen. Alessandra Protti: Has nothing to disclose. Elisabeth Farbu: Received unrestricted grants from Novartis and participated in advisory boards from Biogen, Merck, Novartis, Roche, and Sanofi. Job van Exel: Received research funds from AstraZeneca, GSK, Janssen, Merck, Novartis, Pfizer, Sanofi, and Takeda. Øivind Torkildsen: Received speaker honoraria from and served on scientific advisory boards of Biogen, Sanofi-Aventis, Merck, and Novartis., (Copyright © 2024. Published by Elsevier B.V.)