Myeloid Neoplasm with Eosinophilia Harboring a Novel CCDC6::PDGFRB fusion: Diagnostic Challenge and Therapeutic Implications.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions are rare hematologic malignancies characterized by constitutive kinase activation and sensitivity to tyrosine kinase inhibitors. PDGFRB rearrangements are uncommon, and CCDC6::PDGFRB fusion has been reported only rarely. A 44-year-old man presented with leukocytosis, eosinophilia, anemia, splenomegaly, and constitutional symptoms. A bone marrow examination showed granulocytic hyperplasia with marked eosinophilia. Cytogenetic analysis revealed t(5;10)(q32;q21), while optical genome mapping identified a CCDC6::PDGFRB fusion, confirmed by fluorescence in situ hybridization. No additional pathogenic mutations were detected by targeted next-generation sequencing. Treatment with low-dose imatinib achieved rapid hematologic remission, which was maintained at 22 months. This case highlights the importance of comprehensive genomic testing in patients with eosinophilia-associated myeloid neoplasms for identifying rare and therapeutically actionable PDGFRB rearrangements.