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Myeloid/lymphoid neoplasms with PDGFRB rearrangements are rare hematologic malignancies usually associated with eosinophilia and sensitivity to tyrosine kinase inhibitors, whereas atypical presentations remain poorly defined. We report a 60-year-old man with persistent leukocytosis and thrombocytopenia detected during a routine health examination. Bone marrow examination revealed marked granulocytic proliferation without increased blasts, and peripheral blood showed predominant neutrophilia with only mild eosinophilia. Cytogenetic analysis identified a t(5;14) translocation. RNA sequencing detected an in-frame CCDC88C exon 12::PDGFRB exon 11 fusion, and targeted sequencing additionally identified an ATM frameshift mutation. Treatment with low-dose imatinib (200 mg daily) led to rapid normalization of leukocyte counts within one week and sustained hematologic remission during follow-up. This case broadens the clinicopathologic spectrum of CCDC88C::PDGFRB-rearranged neoplasms and highlights the value of RNA sequencing in identifying actionable kinase fusions in atypical myeloproliferative presentations.