Long-Term Safety and Effectiveness of Mepolizumab 300 mg in Europe (Mepo LTF Study)

This observational study aims to evaluate the long-term effectiveness and safety of mepolizumab 300 mg/4 weeks in adults with eosinophilic granulomatosis with polyangiitis (EGPA) in the European real-life setting. The main questions it aims to answer are: * How effective is mepolizumab 300 mg/4 weeks over long-term follow-up in patients with EGPA? * How safe is mepolizumab 300 mg/4 weeks during long-term treatment? * What are the effects of switching mepolizumab dosage from 300 mg/4 weeks to 100 mg/4 weeks, or from 100 mg/4 weeks to 300 mg/4 weeks? Participants already receiving mepolizumab as part of routine clinical practice. Researchers will retrospectively collect demographic, clinical, laboratory, and treatment-related data from medical records. For patients starting mepolizumab 300 mg/4 weeks, data will be collected from treatment initiation and during follow-up up to 60 months. For patients who change mepolizumab dose, data will also be collected at the time of dose switch and 3 months later.

Inclusion Criteria: * Adult patients with eosinophilic granulomatosis with polyangiitis (EGPA). Patients who meet the 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) Classification Criteria for EGPA or the criteria proposed in the MIRRA trial. * Patients receiving mepolizumab 300 mg/4 weeks, either as the first mepolizumab regimen or after dose escalation from mepolizumab 100 mg/4 weeks. * Availability of at least 3 months of follow-up data after mepolizumab initiation or after dose switch. * Written informed consent. Exclusion Criteria: \- Follow-up shorter than 3 months after mepolizumab initiation or after dose switch.