An acquired stable variant of a dicentric dic(9;20) and complex karyotype in a Syrian childhood B-acute lymphoblastic leukemia case

About 25 years ago, the acquired chromosome abnormality dicentric dic(9;20)(p11 ~ 13;q11) was seen described as a non-random aberration in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Yet, about 200 cases were reported. However, dicentric dic(9;20) is a subtle abnormality which easily may be mixed up with monosomy 20 and/or del(9p). The dicentric dic(9;20) can be found as a sole chromosomal abnormality or can be masked within complex rearrangements; also, a dicentric dic(9;20) is often associated with mono- or biallelic loss of CDKN2A gene. Here we report a case of 16-year-old male diagnosed with a de novo pre-B-ALL. Molecular approaches (array-based multicolor banding (aMCB) and array comparative genomic hybridization (aCGH)) were applied, and a unique complex karyotype involving six chromosomes was identified. It included three previously unreported chromosomal aberrations: dicentric dic(9;20;X), deletion del(7)(p22.2p15.2) and dicentric dic(7;13). The dicentric dic(9;20;X) also led to monoallelic loss of tumor suppressor gene CDKN2A. After successful chemotherapeutic treatment the patient experienced a relapse with a secondary ALL without complex karyotype but a deletion del(19)(p13). Unfortunately, the patient died after 17 months of the initial diagnosis. To the best of our knowledge, a comparable childhood ALL associated with such complex karyotype and deletion del(19)(p13) in secondary ALL was not previously reported. Thus, the complex karyotype with dicentrc dic(9;20;X) seems to indicate for a poor prognosis.

The dicentric dic(9;20) is more common in pediatric ALLs (2%) than in adult cases (< 1%) and seems to be more frequent in females [3]. The median age at diagnosis is 3 years; the median leucocyte count is 20-30 × 10 9 /l [6]; an event-free survival (EFS) and overall survival (OS) up to 5 years are reached by 62 and 82% of the patients, respectively. Accordingly, relapse cases are quite common and post-relapse treatment of many patients was successful [7].
All BCB-ALL cases reported had an immunophenotypes showing positive results for TdT, HLA-DR, CD10, CD19 and CD24, and negative for myeloid markers [1,2,4,5]. The prognostic impact of dicentric dic(9;20) is still unclear, but most reported patients have attained complete remission; thus, such patients are suggested to have a good prognoses [1,2,4,5]. Interestingly, unrecognized dicentric dic(9;20) cases may also be included in cases with monosomy 20 as sole abnormality in ALL; thus, it is noteworthy that the latter is considered to be a favorable prognostic marker [8,9]. Dicentric dic(9;20) can occur as a sole cytogenetic abnormality, or in the context of a more complex karyotype [7]. Common additional genetic changes in ALL with dicentric dic(9;20) are deletions involving chromosome 13q and gains of chromosomes X, 8 and 20 [3,4,7]. Based on data obtained by fluorescence in situ hybridization (FISH) it is known that dicentric dic (9;20) can occur in the presence of the BCR-ABL1 and ETV6-RUNX1 fusion genes [7]. Furthermore, for the CDKN2A (cyclin-dependent kinase inhibitor 2A) gene in 9p21, mono-or biallelic deletions were also repeatedly seen [10,11].
We present here clinical, cytogenetic and molecular data of bone marrow cells obtained from a de novo childhood pre-B-ALL case with a complex karyotype and relapse, involving a variant dicentric dic(9;20).
He was diagnosed as having pre-B-ALL according to the World Health Organization (WHO) classification. Thus, the patient was treated further according to GRALL 2003 chemotherapy protocol. Two days after initiating GRALL 2003 chemotherapy, the patient developed neutropenia, was given Neupogen and restarted chemotherapy protocol. The patient suffered from neutropenia and fever many times during chemotherapy. All chromosomal aberrations were vanishing during the chemotherapeutic treatment. After 17 months of treatment the patient relapsed. BM aspiration revealed 10% of lymphoblasts and PB showed: WBC 1.7 × 10 9 /l (neutrophils 60.5%, lymphocytes 32.2%, and immature cells 7.3%); Hb = 13.6 g/dl; and platelets = 216 × 10 9 /l. The patient received cytosar 3.5 g (twice per day for 4 days) and doxorubcin 50 mg/m 2 for 3 days and a wide spectrum of antibodies.
Approximately 2 months after relapse patient died due to respiratory and heart arrest, as well as neutropenia.
No autopsy was performed. Patient's father agreed with scientific evaluation of his case and the study was approved by the ethical committee of the Atomic Energy Commission, Damascus, Syria.

Discussion and conclusions
According to the literature, the dicentric dic(9;20) has been reported in 199 ALL cases listed in Mitelman database [3]. Dicentric dic(9;20) with trisomy of chromosomes 8 or 21 were seen in 10 and 7 ALL cases, respectively [3]. A translocation t(X;9) involving short and/or long arms of these chromosomes has been found in 11 ALL cases [3]. In addition, partial deletion of the short arm of chromosome 7 [del(7)(p14p11)], and derivative del(19)(p13) were previously reported in 2 and 102 ALL cases, respectively [3]. Interestingly, translocation t(X;20)(p21;p12), derivative del(7)(p22p15), dicentric dic(7;13) have never been described in ALL cases. To the best of our knowledge, a combination of all these complex rearrangements with new formation of dicentric dic(9;20) in one ALL case at diagnosis was not previous reported yet [3].
The dicentric dic(9;20) can be found as a sole chromosomal aberration (~40% of the ALL cases) or with additional chromosomal aberrations (ACAs) (60% of the ALL cases) [17]. Strefford et al. [11] have suggested that the dicentric dic(9;20) is not associated with a recurrent gene rearrangement. While Coyaud et al. [18] noted that dicentric cases can masking a complex rearrangement. Our present case represents a novel formation of dic (9; 20) with loss 9p and 20q in a chromosomal aberration involving X-chromosome.
Notably, the dicentric dic(9;20)-positive leukemia is frequently associated with hetero-or homozygous loss of CDKN2A gene in 31% of all cases analyzed by FISH [17]. However, whether loss of function of this gene is pathogenetically and/or clinically important in dicentric dic(9;20)-positive ALL, remains to be elucidated, but is most likely valid [17]. Other common ACAs included gains of X and 21, both of which are frequent in other subtypes of BCP-ALL [6].
A complex karyotype has been generally classified as ≥3 unrelated chromosomal abnormalities in ALL cases with the absence of established translocations (t [9;22] [19]. Moorman et al. [19] demonstrated that those ALL patients with complex karyotype ≥4 or more unrelated chromosomal abnormalities had a poor outcome in terms of OS and EFS, with most of the relapses occurring in the first 2 years after diagnosis. While, Motll'o et al. [20] showed that a complex karyotype was not associated with adverse prognosis in adult ALL patients treated with risk-adapted or subtype-oriented protocols. In conclusion, we report the first pre-B-ALL case obtained complex karyotype with a new acquired stable variant of a dicentric dic(9;20) resulting from masked partial trisomy 20. In addition, monoallelic deletion of tumor suppressor gene CDKN2A and subsequent deletion del(19p13) without all the previously observed changes in the secondary ALL were seen. Overall, such complex chromosomal changes seem to have adverse prognosis in pre-B-ALL.