<scp>MDS</scp> / <scp>MPN</scp> With <scp> <i>SF3B1</i> </scp> Mutation and Thrombocytosis but Without Ring Sideroblasts

A 75-year-old man presented with extreme weakness and fatigability. On physical examination, there was no hepatomegaly or splenomegaly. He was found to be anemic with thrombocytosis. His blood count showed a white cell count of 3.46 × 109/L, hemoglobin concentration 94 g/L, mean corpuscular volume 91.6 fL, mean corpuscular hemoglobin 28.1 pg., and platelet count 881 × 109/L. Blood smear examination showed marked thrombocytosis and occasional hypochromic erythrocytes, but no other abnormalities. A bone marrow aspirate showed a mildly hypercellular marrow for the age of the patient with a myeloid: erythroid ratio of 3:1. Megakaryocytes were increased and of normal size with reduced lobulation (top left image ×40, top right ×100, May–Grünwald–Giemsa). Storage iron was increased (Grade 5/10) but, although siderotic granules were increased, a careful search disclosed no ring sideroblasts. Trephine biopsy sections showed hypercellularity with increased megakaryocytes, mostly with hypolobated or nonlobated nuclei (lower image, hematoxylin and eosin ×100) and Grade 2/4 reticulin fibrosis. His platelet count remained persistently elevated, between 850 and 1100 × 109/L. Ultrasonography and computed tomography showed the spleen to be of normal size. Next-generation sequencing (NGS) demonstrated a missense mutation in SF3B1, p.(Lys666Med) and frameshift insertions in ASXL1, p.(Gly646TrpfsTer12), and STAG2, p. (Glu750AsnfsTer2). Variant allele frequencies were 43%, 24%, and 30%, respectively. No mutation was detected in BCR, ABL1, JAK2, CALR, or MPL. The disease features demonstrated did not meet the World Health Organization (WHO) criteria for myelodysplastic/myeloproliferative neoplasm (MDS/MPN) with SF3B1 mutation and thrombocytosis as the presence of at least 15% ring sideroblasts is regarded as an essential diagnostic criterion [1]. Nor were the criteria for essential thrombocythemia met. Assignment is necessarily to the category MDS/MPN NOS (unclassifiable) [2]. In the International Consensus Classification (ICC), however, assignment to the category MDS/MPN with thrombocytosis and SF3B1 mutation can be made as the presence of ring sideroblasts is regarded as “common but no longer required” for diagnosis [3]. With the move towards increasingly molecular criteria for classification of hematologic neoplasms the ICC criteria might be favored. The authors declare no conflicts of interest. No further data are available.