PDGFR-β Rearranged Myeloid/Lymphoid Neoplasm With Eosinophilia and Monocytosis in a Toddler Managed Successfully With Imatinib Therapy

Background: Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase fusion gene (MLN-TK) are rare in children and exceptionally uncommon in infants. We report a 17-month-old girl diagnosed with MLN-TK. Observations: She presented with pallor, splenomegaly, anemia, leukocytosis, thrombocytopenia, eosinophilia, and monocytosis. Bone marrow showed hypercellularity with myeloid predominance and increased eosinophilic precursors without excess blasts. Fluorescence in situ hybridization demonstrated PDGFR-β rearrangement in 84% of cells, and karyotyping identified t(5;9)(q32;q34). Imatinib led to a molecular response by 3 months and sustained remission at 3 years of follow-up. Conclusion: This case highlights the importance of early molecular testing in infants with eosinophilia and monocytosis, enabling the use of targeted therapy.