Hematopoietic neoplasm associated with abnormal proliferation of eosinophilic precursors, e.g., cytogenetics for mutations BCR:ABL1, FIP1L1-PDGFRA, PDGFRB, JAK2, FGFR1, and KIT. Failure to detect the FIP1L1:PDGFRA fusion gene does not necessarily rule out the diagnosis of clonal hypereosinophilia. The gene discussed is PDGFRB; the disease is hematopoietic and lymphoid cell neoplasm.