In contrast to other antieosinophilic biologics, mepolizumab is approved for use in other conditions, namely chronic rhinosinusitis with nasal polyps (CRSwNP) [100], eosinophilic granulomatosis with polyangiitis (EGPA) [101,102], and FIP1L1-PDGFRA-negative hypereosinophilic syndrome (HES) [103]. The gene discussed is FIP1L1; the disease is eosinophilic granulomatosis with polyangiitis.