Clonal eosinophilia is associated with myeloid or lymphoid neoplasms harboring PDGFRA, PDGFRB, or FGFR1 rearrangements, Philadelphia-negative myeloproliferative neoplasms, acute myeloid leukaemia, and B- or T-lymphoblastic leukemia/lymphoma featuring marked eosinophilia. The gene discussed is PDGFRB; the disease is acute myeloid leukemia.