BCR-JAK2 fusion

No abstract available

HE requires a wide diagnostic evaluation with a multidisciplinary approach and the development of working groups in order to avoid these inconclusive diagnosis (12% in our series) and the missing diagnostic tests. Our study suggests the association between elevated LDH, cobalamins and tryptase and clonal cause of HE, as well as a higher rate of fibrosis, medullary dysplasia and altered karyotypes in these patients, indicating the need to include these evaluations in the diagnostic process. The group of PDGFRα patients had good prognosis with imatinib, but one patient presented clonal evolution and blastic transformation, showing the clinical challenge of these entities.

Disease progression was also characterized by adaptation to an activated B-cell receptor (BCR)-like signaling phenotype, with marked upregulation of genes such as CD79A, CD79B, IGLL1, VPREB1, BLNK, ZAP70, RAG1, and RAG2. In summary, IKZF1 deletion and a switch from cytokine dependence to activated BCR-like signaling phenotype represent putative mechanisms of ruxolitinib resistance in this case, recapitulating preclinical data on resistance to JAK inhibition in CRLF2-rearranged Philadelphia chromosome-like acute lymphoblastic leukemia.

The patient was initially treated with hydroxycarbamide pending approval for ruxolitinib whilst being worked up for allogeneic stem cell transplant...JAK2 fusions are thought to be associated with a more aggressive clinical course than other chronic myeloid malignancies, and as such allogeneic stem cell transplant is considered the most appropriate treatment where possible, with ruxolitinib being utilised as a bridge to transplant, by improving remission rate prior to the transplantation. Given the distinct clinical and pathological characteristics, as illus- trated in this case, we believe testing for a JAK2 fusions should be considered in otherwise unclassifiable myeloid / lymphoid neoplasms, especially those with eosinophilia.

We describe the use of chromosomal microarray analysis (CMA), fluorescence in situ hybridization (FISH) with a probe for JAK2, and genomic mate pair analysis to describe a complex karyotype with a t(9;22) that produced a functional BCR-JAK2 fusion, leading to the appropriate diagnosis for the patient. This case highlights the importance of using an integrated genomic approach to fully define complex aberrations to assign proper diagnoses.