In the case of eosinophilia, FISH/cytogenetics and molecular analysis (on bone marrow aspirate or peripheral blood cells) should specifically look for PDGFRA, PDGFRB, FGFR1, FLT3, ETV6, and JAK2 gene rearrangements (Figure 3). The gene discussed is FLT3; the disease is Increased total eosinophil count.