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A case of pediatric B-Lymphoblastic leukemia presenting with a t(9;12)(p24;q11.2) involving JAK2 and concomitant MLL rearrangement with apparent insertion at 6q27

2013-11-30 15:23:10

Biomarker Research; 2013, 1:31; DOI:10.1186/2050-7771-1-31



Carlos A Tirado, David Shabsovich, Matthew DeNicola, Dinesh Rao, Lynn Yang, Rolando Garcia and Nagesh Rao



Abstract



Background



B-cell acute lymphoblastic leukemia (B-ALL) is the most common malignancy in pediatric patients and the leading cause of cancer-related death in children and young adults. Translocations of 9p24 involving JAK2 (9p24) and gain-of-function mutations of JAK2 with subsequent activation of the JAK2 kinase have been described in several hematological malignancies including B-ALL. However, rearrangements involving JAK2 are rare in B-ALL as only few cases have been described in the literature.



Findings



Herein, we present a case of pediatric B-ALL whose conventional cytogenetics revealed an abnormal karyotype with a reciprocal translocation involving 9p24 (JAK2) and 12p11.2. Fluorescence in situ hybridization (FISH) studies using the RP11-927H16 Spectrum Green JAK2 probe on previously G-banded metaphases confirmed the involvement of JAK2 in this rearrangement. Further FISH studies on the same previously G-banded metaphases using the LSI MLL probe helped to characterize an insertion of MLL into 6q27 as an additional abnormality in this karyotype. FISH studies performed on interphase nuclei also revealed an abnormal clone with MLL rearrangements in 23.6% of the nuclei examined as well as an abnormal clonal population with a deletion of the 5'IGH@ region in 88.3% of the nuclei examined.



Conclusions



Rearrangements of 9p24 can result in constitutive activation of JAK2, and have been observed in B-ALL. Rearrangements of the MLL gene have also been described extensively in B-ALL. However, rearrangements of MLL with a partner at 6q27 and in conjunction with a translocation involving JAK2 have not been previously described. This case pinpoints the importance of FISH and conventional cytogenetics to characterize complex rearrangements in which JAK2 and MLL are involved. The therapeutic targeting of JAK2 and MLL in cases like this may be prognostically beneficial.



Introduction



Abnormalities involving JAK2 (9p24) have been seen in B-ALL, but most often via point mutations involving the pseudokinase domain, R683. Rearrangements of 9p24, however, are rare, with only a small number of cases reported in the literature involving the following loci and partner genes: 22q11.2 (unknown gene), 12p13 (ETV6), 5p14.1 (SSBP2), 8p22 (PCM1), and 9p13.2 (PAX5). Activation of JAK2 occurs via gene fusions encoding chimeric proteins in which the kinase domain of JAK2 is fused to another cellular gene that provides a dimerization or oligomerization interface to the JAK2 kinase domain, leading to constitutive activation. This case pinpoints the fact that JAK2 rearrangements may play an important role in the pathogenesis of lymphoblastic leukemias. To the best of our knowledge, this is one of the few cases with rearrangements of JAK2 with chromosome 12p11.2 as well as rearrangements of MLL involving chromosome 6q27, both with unknown partner genes.



Case Presentation



A 13-year-old male presented with abdominal pain and fevers for three months. He was found to have leukocytosis (WBC 76.5x103/uL), anemia (Hgb 5.3 g/dL), and thrombocytopenia (platelet count 15.3x103/uL). Flow cytometry on peripheral blood revealed 94% blasts which expressed bright CD10, CD19, partial CD20, CD34, partial CD38, partial TdT, CD79a, and HLA-DR. A bone marrow biopsy showed a hypercellular marrow extensively involved (~95%) by sheets of lymphoblasts. These findings are consistent with a diagnosis of B-lymphoblastic leukemia. The patient was immediately started on induction chemotherapy with AALL0232 high-risk ALL chemotherapy protocol. A follow-up bone marrow biopsy on day 29 showed minimal residual disease (MRD). A normal karyotype was seen in all metaphase cells examined and loss of one copy of the 5'IGH@ was the only abnormality detected in 2.7% of the interphase nuclei studied. The patient subsequently was given treatment per clinical trial AALL0031 and achieved primary remission. Most recently, the patient received a successful allogeneic bone marrow transplant from a female donor.



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