Myeloproliferative Neoplasm with BCR-JAK2 Fusion Gene As the Result of t(9;22)(p24,11.2) in a Brazilian Patient

Chronic Myeloid Leukemia (CML) is the most well described disease result of t(9;22)(q34,q11.2). This chromosomal rearrangement leads to well-know BCR-ABL fusion that promotes tyrosine kinase activity. There are others oncogenic BCR fusion found such as PDGFRA (4q12), FGFR1(8p12) that causes myeloproliferative disorders (MD).

JAK2 gene is one of the 4 genes members of JAK family. The JAK2 V617F mutation which results from a G –>T transversion at nucleotide 1849 in exon 14 of the JAK2 gene, the consequence of which is substitution of valine by phenylalanine at codon 617 is associated with MD and it is a major diagnosis criterion for Primary Myeloficrosis, Polycythaemia vera and Essential thrombocytemia. There are described a lot chromosomal translocations involving the JAK2 locus.

We report an extremely rare case with BCR-JAK2 fusion gene as the result of t(9;22)(p24,q11.2) for the first time in Brazilian people, and it is the 6^thcase all of the world.

In April 2010, a 54 years old male patient presented fatigue, abdominal pain and splenomegaly. A blood count revealed leukocytosis 93.380/mm³ with a predominance of neutrophils and left shift. Conventional cytogenetic analysis was performed and it was evidenced 46,XY, t(9;22)(p24;q11.2) in 90% metaphases examined, due to expected association it was promoted BCR-ABL1 fusion gene and it was not detected by using RT-PCR. He was treated with imatinib 400mg/day because the involvement of BCR gene. After three months he presented weight loss, progressive splenomegaly without hematologic response and it was modified to Dasatinib 150mg/day plus hydroxyureia 3g/day. In August 2011, due to not hematologic response, it was stopped Dasatinib treatment and nowadays patient has been treating with hydroxyureia 1.5g/day. His last follow up in May 2012, blood count was abnormal Hb 16.8g/dl leukocytes 7730/mm³ and low platelets count 32.000/mm³. The differential count showed 65.3% segmented granulocytes, 13.6% eosinophlis, 1.6% basophil, 2.6% monocytes, 16.9% lymphocytes.

It was repeated conventional Karyotyping and it was evidenced 46,XY, t(9;22)(p24;q11.2) in all of metaphases examined. The presence of BCR-ABL rearrangement was excluded by using the fluorescence in situ hybridization (FISH) using a BCR-ABL probe. In addition, it was not evidenced FIP1L1-PDGFRa fusion gene and JAK2 V617F mutation by using RT-PCR.

We have described a male patient with MD with t(9;22)(p24;q11.2) wich leads to the BCR-JAK2 fusion and it was not evidenced BCR-ABL1, FIP1L1-PDGFRa fusion genes and JAK2 V617F mutation by using RT-PCR. Moreover, patient has not been achieved hematologic response with tyrosine kinase inhibitors: imatinib and dasatinib. In the five cases reported three presented MD, one Acute Myeloid Leukemia and one Acute Lymphoblastic Leukemia. Only in one case report it was prescribed imatinib and the patient lost the follow up (Table1). The BCR-JAK2 fusion protein contain the coiled-coil dimerization domain of BCR and the protein tyrosine Kinase domain (JH1) of JAK2. It was not possible to define what would be the best therapy, because tyrosine kinase inhibitors may not be effective to the BCR-JAK2 fusion. Maybe in MD presentation, we could return to pre- tyrosine kinase inhibitors era based on treatments with hydroxyureia, subcutaneous cytarabine and interferon for patients that were not potential candidates for allogeneic transplant.

No relevant conflicts of interest to declare.