Efficacy and safety of azacitidine for VEXAS syndrome: a large-scale retrospective study from the FRENVEX group.

VEXAS (Vacuoles, E1 Enzyme, X-Linked, Autoinflammatory, Somatic) syndrome is a severe monogenic disorder caused by somatic UBA1 mutations, characterized by inflammation, cytopenias and frequent association with myelodysplastic neoplasms (MDS). Steroid dependence is common, and targeted therapies have demonstrated limited efficacy. Azacitidine (AZA), a hypomethylating agent used in MDS, has shown potential in VEXAS but data remain limited. This multicenter retrospective study assessed AZA efficacy and safety in 88 genetically confirmed VEXAS patients from the FRENVEX (French VEXAS) group, 80% meeting WHO 2022 MDS criteria. Inflammatory response rates were 41% at 6 months and 54% at 12 months, regardless of MDS status. A total of 50 (61%) patients achieved inflammatory response, with 70% occurring at 6 months, suggesting a delayed median response. Among responders, relapse-free survival on AZA was 90% at 1 year and 85% at 5 years. Of the 12 responders who discontinued AZA, 9 relapsed after a median of 3.1 years (range: 0.4-5.6), with effective re-exposure in 4 of 5 patients. Hematological responses included red blood cell transfusion independence in 65% and platelet improvement in 77% of patients. Molecular response, defined as a ≥25% reduction in UBA1 variant allele frequency (VAF), was observed in 65% of patients, all of whom achieved inflammatory and hematological responses; and VAF dropped below 2% in 43% of cases. Infections (34%) and cytopenias (36%) were common, particularly during the first three cycles. This study establishes AZA as an effective therapy for VEXAS, improving inflammation, cytopenias, and UBA1 clonal burden, warranting larger prospective trials.