Transformation of myelodysplastic syndrome with isolated 5q-syndrome to chronic myelogenous leukemia with a novel complex BCR/ABL1 translocation with rapid progression to blast crisis

We report a case of a 72 year old female who was referred to our institution in August 2010 for Myelodysplastic syndrome (MDS) with a deletion of part of the long arm of chromosome 5 [i.e., del(5) (q12q33)]. In June 2014, she transformed to Chronic Myelogenous Leukemia (CML), where cytogenetic and FISH analysis of the bone marrow (BM) revealed the del(5q) in 1.5% of nuclei and a complex BCR/ABL1 translocation [i.e., 45,XX,t(9;15;22)(q34;p10;q11.2),-22]. Six weeks later, in July 2014, she transformed to an Acute Myelogenous Leukemia (AML) blast crisis. RT-PCR was positive for BCR/ABL1 transcript. The patient was treated with a tyrosine kinase inhibitor, Nilotinib, then had a haploidentical allogeneic bone marrow transplant from her son, and was in remission after treatment. However, throughout the course of nine subsequent cytogenetic analyses, the patient continued to undergo clonal chromosome evolution, even during remission. Transformation from MDS del(5q) to CML with rapid progression to blast crisis has rarely been reported. To our knowledge, transformation with this complex translocation has never been described. Here we describe these rare cytogenetic findings and discuss possible mechanisms involved in the persistent and evolving clonal cytogenetic abnormalities seen during the clinical course of the disease.


Introduction
Myelodysplastic syndrome (MDS) is a group of clonal hematopoietic stem cell disorders that are characterized by peripheral blood cytopenias, dysplastic morphology, and clonal cytogenetic abnormalities. The majority of clonal cytogenetic abnormalities reported in 30% to 50% of MDS are monosomy 7, loss of Y, del(5q), del(7q), del(20q) and trisomy 8.
MDS with isolated 5q-syndrome is characterized by anemia, with or without other cytopenias, and a deletion of part of the long arm of chromosome 5. Patients with MDS with 5qsyndrome have a good prognosis and are usually monitored without treatment [1,2].
Multiple genetic abnormalities occur during the evolution of MDS. BCR/ABL1 rearrangements occur with a frequency of 1% (5). To our knowledge, this complex BCR/ABL1 translocation has never been reported. We present a case of MDS transforming to CML with a complex BCR/ABL1 translocation followed by rapid progression to an AML blast crisis.

Case presentation
A 72 year old female presented to an outside institution in 2007 and was diagnosed with MDS with isolated del(5q). Her care was transferred to our institution in August 2010, where G-banded chromosome analysis of the bone marrow (BM) Hematology and Leukemia ISSN 2052-434X | Volume 4 | Article 2 CrossMark ← Click for updates doi: 10.7243/2052-434X-4-2 revealed a deletion of part of the long arm of chromosome 5 [i.e., del(5)(q12q33)] in 11/20 metaphase cells and was confirmed by FISH ( Table 1). The complete blood count (CBC) of the peripheral blood showed anemia ( Table 2).
Seven weeks later, in July 2014, her CBC still showed anemia, leukocytosis, and thrombocytosis, but now there were 14% blasts in the peripheral blood and 18% blasts by flow cytometry of the BM. Her disease transformed from CML chronic phase into a myeloid blast crisis. This was a rare occurrence of rapid transformation from MDS to CML to blast crisis. The patient was treated with Nilotinib, a tyrosine kinase inhibitor. The patient had a haploidentical allogeneic bone marrow transplant from her son. After completing treatment, the patient was in morphologic remission, with normal marrow morphology and cellularity. However, she continued to undergo cytogenetic clonal chromosomal evolution (Figure 1 and Table 1).
To our knowledge, this is the first report of MDS transformation to CML followed by rapid progression to an AML blast crisis with this complex BCR/ABL1 translocation.

Materials and methods
Cytogenetic G-band metaphase analysis and fluorescence in situ hybridization (FISH) were performed using standard cytogenetic techniques on bone marrow (BM) and unstimulated Flow cytometry was performed using a Becton Dickinson FACSCalibur using BD anti-CD33 (340679) and anti-CD34 (340667). Blood counts were performed using a Sysmex XN-10. BCR/ABL1 (p210) fusion transcript was quantified by RT-qPCR utilizing the Xpert BCR-ABL monitor kit, Cepheid, San Jose, CA. RNA was extracted from the patient's peripheral blood with the QIAamp RNA blood minikit, Qiagen, Germany. The RNA was reverse transcribed and then amplified by realtime-PCR with the Light-Cycler. BCR/ABL1 was quantified by using the t(9;22) quantification kit from Roche Molecular Systems Inc, Branchburg, NJ (this kit does not distinguish between p210 and p190).

Results
In 2007, the patient presented with MDS with 5q-syndrome at an outside institution. In August 2010 at our institution, morphologic evaluation of the BM was consistent with MDS and G-banded chromosome analysis revealed a deletion of  Table 1). In June 2014, bone marrow biopsy showed a hypercellular marrow with left-shifted granulocytic and megakaryocytic hyperplasia, consistent with transformation to CML in chronic phase (Figure 2). Cytogenetic and FISH analyses of the BM revealed the del(5q) in 1.5% of nuclei and a complex BCR/ ABL1 translocation: 45,XX,t(9;15;22)(q34;p10;q11.2),-22 in all metaphase FISH cells (Figure 3, Table 1).

Figure 2. CML, chronic phase.
Histologic examination of the bone marrow with hematoxylin-eosin staining reveals hypercellular marrow space with left-shifted myeloid hyperplasia and dwarf megakaryocytes. Arrow indicates a dwarf megakaryocyte.
Seven weeks later in July 2014, she was in blast crisis with 14% blasts in the peripheral blood (PB) and 18% blasts by flow cytometry of the BM. G-banding and FISH of unstimulated blood (UB) revealed both the complex translocation and further clonal evolution. An additional der(15)t(9;15;22) (q34;p10;q11.2) in 5/20 metaphase cells was observed. RT-PCR molecular testing showed a p210 BCR/ABL1 transcript level of >10% ( Table 3). The del(5q) was not present in this analysis. The patient transformed from CML to myeloid blast crisis in less than a month.
Twelve weeks later in November 2014, cytogenetic and FISH analysis of the remission BM revealed the same clones  In December 2015, she developed a rash and was diagnosed with Graft-versus-Host Disease (GVHD) treated with photophoresis. Her most recent bone marrow biopsy from January 2016 showed trilineage engraftment and no morphologic and no immunophenotypic evidence of MDS, AML, or CML. However, BCR/ABL1 was present in the chromosomes FISH and by RT-PCR (Tables 1 and 3, Figure 4).

Discussion
The transformation from MDS to CML has rarely been reported [6]. To our knowledge, this is the first report of rapid progression to CML myeloid blast crisis with a complex BCR/ABL1 translocation [45,XX,t(9;15;22)(q34;p10;q11.2),-22] (Figure 1) in this clinical scenario. The patient had clonal cytogenetic evolution with chromosomal gains and losses of diverse cell populations during the various phases of therapy and during remission. AML has been proposed to arise from Class I and Class II mutations. Class I mutations increase cell proliferation and survival, whereas Class II mutations suppress differentiation and apoptosis. BCR/ABL1 is a Class II mutation that impairs differentiation and apoptosis [3]. In AML, cooperation of Class II mutations suppressing differentiation with Class I mutations increasing cell proliferation are frequently seen with BCR/ABL1 positive subclones in patients with AML. This was reported in a small series of patients by Bacher et. al., 2011 [4]. These subclones occurred in various subtypes of AML and one patient had del(5q). It is possible that the BCR/ABL1 translocation could cooperate with different mutation types in AML as a Class I mutation promoting cell proliferation of the abnormal clones. As the BCR/ABL1 translocation only occurs in approximately 1% of patients with AML [5], this may be significant for cell proliferation.
The BCR/ABL1 translocation occurs in <1% of MDS patients [5]. The few reported cases support evidence that the process represents multistep leukemogenesis. The initial event may result from clonal proliferation of stem cells in the acquisition of the translocation existing in neoplastic cells [6]. Some patients with AML may acquire the translocation as an additional chromosome abnormality during the evolution of the disease or during relapse, as reported by Bacher [4] and seen in our patient. Three possible explanations for the late appearing BCR/ABL1 translocation are: 1. It may have been present during the course of the patients' disease, but the patient was not cytogenetically evaluated for four years. 2. It may represent evidence of a multistep process. 3. The translocation may represent a new clone in leukemic relapse [6][7][8][9]. These findings indicate that the translocation could have arisen during various times within the overall course of the disease. The patient went from MDS to CML to an AML-like blast crisis within one month. To our knowledge, this was the first report associated with this complex BCR/ABL1 translocation: 45,XX,t(9;15;22)(q34;p10;q11.2),-22 with rapid progression resulting in the loss and gain of diverse cell populations. This case illustrated the importance of careful patient monitoring to diagnose the nature of this disease and to accordingly modify the course of treatment. Additional cases of MDS with complex BCR/ABL1 translocations are needed to further determine the clinical significance of these findings.