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Letters to the Editor
All six ETV6-ABL1 rearranged patients showed myeloid proliferation and eosinophilia, a common char- acteristic of ETV6 rearranged myeloid neoplasms, such as ETV6-PDGFRA, ETV6-PDGFRB, and ETV6-JAK2.15 Review of the literature identified 21 additional cases of MPN and four cases of AML with ETV6-ABL1 fusions
(median age 48 years, 18 male, 7 female) (Online Supplementary Table S3). PB absolute eosinophilia was reported in 13 of 14 patients who had available data for evaluation. Interestingly, 8 of 14 patients also had periph- eral basophilia (defined by >1% basophils). Six out of 21 MPN cases with ETV6-ABL1 rearrangements progressed
D
K
A
BC
EFHI
GJ
Figure 1. Myeloid neoplasms with ETV6-ABL1 fusions. (A) Hematoxylin & Eosin staining of a bone marrow biopsy specimen (Patient 4) showed hypercellularity, increased M:E ratio, highly variable megakaryocytes morphology, predominantly large in size. (B) Immunohistochemistry showed markedly increased phospho- STAT5 signals but not phospho-STAT3 (inset). (C) Immunohistochemistry showed mildly increased phospho-ERK1/2 signals. (D) Schematic illustration of ETV6- ABL1 fusions, bidirectional RNA sequencing reads, and transcript sequence of the in-frame fusion product detected by Archer FusionPlex with exons 1-5 of ETV6 fused to exons 2-11 of ABL1. (F-K) Flow cytometry sorted cell populations, including CD34+CD38– (enriched for hematopoietic stem cells, HSC), CD34+CD38+ (hematopoietic progenitors/blasts), monocytes, granulocytes and lymphocytes (Lym) (F and I). Fluorescence in situ hybridization (FISH) analysis with an ETV6 break-part probe set (Abbott Molecular) shows a split ETV6 signal pattern. The 5′ and 3′ ETV6 were labeled with green and red, respectively. ETV6 rearrangement was observed in CD34+CD38– (G), CD34+CD38+ (H), monocytes (J), and granulocytes (K) but not in mature lymphocytes (inset in I). (L) A summary of ETV6 FISH results on flow sorted cell populations from two patients. n/a: not available.
haematologica | 2021; 106(2)