A 22-year-old woman presented with fatigue and leukocytosis without organomegaly and a referral diagnosis of chronic myeloproliferative neoplasm without BCR::ABL1 translocation or JAK2 mutation. Complete blood count showed leukocytosis (white blood cell [WBC], 21.8 × 10⁹/L), anemia (hemoglobin, 11.1 gm/dL), and thrombocytopenia (platelets, 114 × 10⁹/L) with neutrophilia (15.9 × 10⁹/L), eosinophilia (1.74 × 10⁹/L), and rare circulating blasts. Bone marrow (BM) biopsy was hypercellular (∼100%) with myeloid hyperplasia, atypical megakaryocytic hyperplasia, and clusters of foamy histiocytes (panel A, ×400, hematoxylin-eosin stain) highlighted with periodic acid–Schiff stain with fast green counterstain (panel B, ×400). BM smears showed left-shifted myeloid hyperplasia with numerous pseudo-Gaucher cells/sea blue histiocytes with abundant blue and variably lamellar cytoplasm (panel C; ×1000, Wright-Giemsa). Karyotyping detected a t(5;12) (panel D), and fluorescence in situ hybridization confirmed the presence of PDGFRB (panel E) and ETV6 rearrangement in 78% of analyzed cells. The patient was treated with imatinib (400 mg daily) and achieved remission with a WBC of 8.9 × 10⁹/L at 1-month follow-up.

Sea-blue histiocytes and pseudo-Gaucher cells are a hallmark of increased cell turnover and characteristically associated with chronic myeloid leukemia BCR::ABL1+. To our knowledge, this is the first report describing increased pseudo-Gaucher cells in association with a myeloid neoplasm with eosinophilia and PDGFRB rearrangement, expanding the spectrum of this morphologic finding.