Numerous ring sideroblasts in chronic neutrophilic leukemia

A 72-year-old man was admitted to the hospital with anemia and bilateral lower-extremity edema for 2 months. Anemia had once been noted 5 years ago. Laboratory findings showed white blood cells 31.08 × 10⁹/L (86% neutrophils, 1% myelocytes, 4% metamyelocytes, 1% monocytes, 8% lymphocytes), hemoglobin 68 g/L, platelets 96 × 10⁹/L (panel A; Wright-Giemsa stain, original magnification ×400). Computed tomography scan showed splenomegaly. Bone marrow revealed marked granulocytic hyperplasia with 0.8% blasts but no dysplasia (panel B; Wright-Giemsa stain, original magnification ×1000). Ring sideroblasts comprising 54% of erythroid precursor were identified on iron-stained marrow smear (panel C; Prussian blue stain, original magnification ×1000, arrows; insert D; Prussian blue stain, original magnification ×1000). Bone marrow biopsy showed a predominance of granulocytic cells with grade 2 reticulin fibrosis. Karyotype was 46,XY[20]. BCR-ABL1, JAK2, CARL, MPL were negative. CSF3R T618I/W818X, ASXL1, TET2, and SF3B1 mutations were detected by next-generation sequencing. The diagnosis of chronic neutrophilic leukemia (CNL) was made.

Cases with ring sideroblasts and SF3B1 mutation are usually diagnosed as myelodysplastic syndrome with ring sideroblasts or myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis. CSF3R mutations occur frequently in CNL and are rare in atypical chronic myeloid leukemia (aCML). In our case, the morphological features and CSF3R mutation support CNL rather than aCML or chronic myelomonocytic leukemia. CNL with ring sideroblasts and SF3B1 mutations had not been reported so far, so the significance in CNL is unknown.