Acute lymphoblastic leukemia with e1a3 BCR/ABL fusion protein. A report of two cases

B Acute Lymphoblastic leukemia (B-ALL) with Philadelphia chromosome (Ph?) is a neoplasm of lymphoblast committed to the B cell lineage. The clinical presentation of B-ALL Ph?+ is similar to B-ALL, but is more common in adults than in children. The e1a3 rare variant is produced by the fusion of BCR exon 1 to ABL exon 3. The presence of this translocation has been associated with good disease outcome for chronic myeloid leukemia in a very small series of only 5 cases; there is no such evidence for B-ALL. We report two new cases of B-ALL Ph+ with the rare e1a3 fusion transcript. The e1a3 and e1a2 (p190) transcripts have been reported to have a similar molecular weight and probably a similar clinical profile, thus in these cases the presence of e1a3 was associated with extramedullary infiltration and disease acceleration.

Background

B Acute Lymphoblastic leukemia (B-ALL) with Philadelphia chromosome (Ph?) is a neoplasm of lymphoblast committed to the B-cell lineage. The clinical presentation of B-ALL Ph?+ is similar to B-ALL, but is more common in adults than in children and it has a worse prognosis among patients with B-ALL. The tyrosine kinase BCR-ABL fusion protein is the product of the Philadelphia chromosome, which results from the reciprocal translocation t(9;22)(q34;q11) that juxtaposes the c-abl oncogene 1 on chromosome 9 with the bcr gene on chromosome 22 generating the BCRABL1 oncogene [1-4]. Depending on the location of the breakpoint in BCR, several types of BCR-ABL fusion proteins may appear [5]. To date, three main breakpoint cluster regions in the BCR gene have been reported: the M-bcr region located between exons 12 and 16, the m-bcr located between exons e2? and e2 and the u-bcr located in exon 19. The three more common variants of BCR-ABL described are p210 [more frequent in chronic myeloid leukemia (CML)], p190 (more frequent in B-ALL) and p230 (more frequent in Chronic Neutrophilic Leukemia (CNL) [6-8]. The type of rearrangement in CML is related to the patient clinical course. Other rare forms such as e1a3, b2a3 and e6a2 of BCR-ABL have been described. The e1a3 variant is produced by the fusion of BCR exon 1 to ABL exon 3. The presence of this translocation has been associated with good disease outcome for CML in a very small series of only 5 cases [9, 10]; there is no such evidence for ALL. Moreover, we have reported the first e1a3 case that progressed from CML to a lymphoid blast crisis [1]. Thus, the molecular prognosis of these rare variant forms is still unclear. We report two new cases of B-ALL Ph+ with the rare e1a3 fusion transcript.

Case 1 presentation

The first patient is a 43-year-old male, who consulted our center for night sweats and weight loss in the last 3 weeks. He had no previous history or records in our center. The physical examination was normal except for a slight splenomegaly and the blood test was compatible with hyperleukocytosis, anemia and thrombocytopenia, (leukocytes 136.00 · 109/L, hemoglobin 11.70 g/dl, platelet count 39.70 · 109/L) and 93 % of small-medium sized lymphoblast in the Grunwald-Giemsa blood smear. The bone marrow aspirate examination had an hypercellular infiltration of 90 % which was confirmed by immunophenotype (CD19+, CD10+, CD34+, TdT+, DR+, CD79 alfa+, CD20?, cytoplasm IgM negative). 80 % of the blast cells also expressed CD33+. A fresh sample from the bone marrow aspirate was collected for molecular and cytogenetic analysis. The assay revealed the presence of the following karyotype:46,XY,t(9;22)(q34;q11) [2] /46,XY,del(9)(p22)t(9;22)(q34;q11) [4] /46,XY,del(9)(p22)t(9;22)(q34;q11),del(20)(q13) [5] /46,XY [9]. FISH analysis confirmed the presence of BCR-ABL1 fusion gene (Fig. 1). The patient's RNA was isolated from the peripheral blood and subjected to a two round multiplex reverse transcription and polymerase chain reaction (RT-PCR). In order to avoid RNA quality and/or handling errors, we included an internal positive control in where a 690-bp segment of the ubiquitously expressed transcription factor E2A mRNA was amplified. The primers and PCR conditions used in the first and second round of the nested PCR reaction are described by Pallisgaard et al. [11]. We identified an atypical amplification band of approximately 100 bp, much smaller than the p190 (e1a2) fragment. In order to confirm the presence of a BCR-ABL transcript this band was extracted from the agarose gel, purified and then analyzed by DNA sequencing. cDNA sequence revealed the presence of the e1a3 variant (Fig. 2). [ Table Omitted - see PDF ]

Table 1

Clinical characteristics, therapy and outcome of ALL cases reported with e1a3 fusion protein compared with those presented in this manuscript

#

Age

Leukocite count at Dx

BM infiltration

TKI

SCT

Status

Response

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