Mepolizumab, targeting circulating IL-5, prevents the binding with its receptor on eosinophils and their progenitors and is currently approved by the European Medical Agency for severe eosinophilic asthma, chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis, and HES, but its use in EM is limited to few reported cases.6–8. This evidence concerns the gene IL5 and hypereosinophilic syndrome.