MPRIP::PDGFRB fusion identified in a male patient with a myeloid/lymphoid neoplasm with eosinophilia.

Myeloid/lymphoid neoplasms with eosinophilia (MLN-eo) associated with PDGFRB rearrangements represent a rare but clinically significant category of hematologic malignancies, characterized by clonal eosinophilia and exceptional sensitivity to tyrosine kinase inhibitors. Among these, the MPRIP::PDGFRB fusion is exceptionally uncommon, with only three patients previously reported. Here, we report the first United States patient with MPRIP::PDGFRB fusion in a 34-year-old man presenting with leukocytosis, marked eosinophilia, anemia, thrombocytopenia, mucocutaneous lesions, hepatosplenomegaly, chronic gastrointestinal symptoms, and tree-in-bud pulmonary nodularity. Bone marrow evaluation revealed a markedly hypercellular marrow with increased eosinophils, grade 1 reticulin fibrosis, and dysmegakaryopoiesis. Fluorescence in situ hybridization (FISH) demonstrated a PDGFRB rearrangement in 76% of cells, and chromosome analysis revealed a balanced translocation t(5;17)(q32;p11.2). Next-generation sequencing RNA-based myeloid fusion panel analysis identified an MPRIP::PDGFRB fusion formed by an in-frame junction of MPRIP exon 20 and PDGFRB exon 12. The patient was initiated on imatinib therapy and achieved rapid remission. To contextualize this patient, we compared the clinical and molecular features of all previously published patients with MPRIP::PDGFRB fusion, noting shared findings of marked eosinophilia and excellent imatinib sensitivity, but notable heterogeneity in symptom burden, degree of marrow fibrosis, and associated immune-related manifestations. Additionally, we provide an overview of 45 reported PDGFRB fusion partner genes, summarizing their cytogenetic characteristics, and associated diseases. This case report expands the clinical spectrum of MPRIP::PDGFRB positive MLN-eo and underscores the essential role of cytogenetic and molecular testing in the diagnostic evaluation of eosinophilia, given the significant therapeutic implications of identifying PDGFRB fusions.