Molecular characterization of AML with ins(21;8)(q22;q22q22) reveals similarity to t(8;21) AML

Identification of chromosomal abnormalities and genomic features in near-triploidy/tetraploidy-acute leukemia by fluorescence in situ hybridization

Background

Near-triploidy/tetraploidy is rarely found in acute leukemia. Only limited data are available to characterize this condition, and it remains largely unknown.

Patients and methods

In our study, we performed karyotype analysis on 1,031 patients diagnosed with acute leukemia from 2006 to 2018. A total of 10 patients of near-triploidy/tetraploidy karyotype were enrolled. Two cases of near-triploidy (66-79 chromosomes) and eight cases of near-tetraploidy (84-100 chromosomes) were identified. Bone marrow samples of these 10 patients were analyzed by fluorescence in situ hybridization with 19 commercially available probes that detected a small portion of gene alterations and large regions of chromosome amplifications.

Results

Of the six patients with acute myelocytic leukemia, we detected three cases of double t(8;21)(q22;q22) that have not been previously reported, and one of them demonstrated ins(21;8) (q22;q24q22). We also describe a novel pediatric case carrying double t(15;17)(q22;q21) and receiving targeted treatment with all-trans retinoic acid therapy. To date, this case has responded well to the regimen and has shown continuous complete remission. All patients received chemotherapy. One of them received allogeneic hematopoietic stem cell transplant (HSCT) and survived for 22 months. Eight of the 10 patients died, and the median overall survival was 11 months.

Conclusion

Using fluorescence in situ hybridization, we identified the distinct complex karyotype of near-triploidy/tetraploidy and provided further prognostic information. Tetraploidy acute promyelocytic leukemia had favorable prognosis; thus, HSCT was not necessary. The case of insertion t(21;8)(q22;q24q22) in tetraploidy responded poorly to chemotherapy and achieved molecular remission with difficultly. Data from patients in this group indicated that near-triploidy/tetraploidy acute leukemia has poor prognosis and new therapy is urgently needed.

A novel insertion ins(18;5)(q21.1;q31.2q35.1) in acute myeloid leukemia associated with microdeletions at 5q31.2, 5q35.1q35.2 and 18q12.3q21.1 detected by oligobased array comparative genomic hybridization

BACKGROUND

Nonrandom clonal chromosomal aberrations can be detected in approximately 55% of adult patients with acute myeloid leukemia (AML). Recurrent cytogenetic abnormalities play an important role in diagnosis, classification and prognosis of AML. However, several chromosomal abnormalities have not been completely determined or characterized, primarily because of their low incidence and limited amount of data.

RESULTS

We characterized an AML patient with a novel apparently balanced insertion ins(18;5)(q21;q31.2q35.1) that was cryptic by G-banding. The rearrangement was further examined by molecular cytogenetic methods and oligobased high-resolution array CGH (oaCGH) analysis. We show that an approximately 31.8 Mb large segment from chromosome 5 bands q31.2 to q35.1 has been inserted, by a direct mechanism, into chromosome 18 between bands q12.3 and q21.1. The insertion was unbalanced with concurrent submicroscopic deletions at 5q31.2 (approximately 0.37 Mb in size), 5q35.1q35.2 (approximately 1.98 Mb in size), and 18q12.3q21.1 (approximately 2.07 Mb in size). The microdeletions affect genes on 5q and 18q that have been associated with hematological malignancy and other cancers. A novel juxtaposition of the genes NPM1 and HAUS1 at 5q35.1 and 18q21.1, respectively, was detected by FISH analysis. Searching the literature and the Mitelman database revealed no previously reported ins(18;5) cases. Interestingly, however, two AML patients with translocation t(5;18)(q35;q21) encompassing the 5q35 and 18q21 breakpoint regions as detected in our present ins(18;5) patient have been reported.

CONCLUSIONS

It is well-known that cytogenetic abnormalities on the long arm of chromosome 5 affect hematopoiesis. However, the precise mechanism of their involvement in myeloid transformation is elusive. Our present data shed new light onto the frequent abnormalities on 5q as well as to the less frequent abnormalities observed on 18q in myeloid malignancies. In addition, we show that oaCGH analysis is a useful adjunct to revealing submicroscopic aberrations in regions of clinical importance. Reporting rare and nonrandom chromosomal abnormalities contribute to the identification of the whole spectrum of cytogenetic abnormalities in AML and their prognostic significance.

Diagnostic and prognostic value of cytogenetics in acute myeloid leukemia

The last 4 decades have seen major advances in understanding the genetic basis of acute myeloid leukemia (AML), and substantial improvements in survival of children and young adults with the disease. A key step forward was the discovery that AML cells harbor recurring cytogenetic abnormalities. The identification of the genes involved in chromosomal rearrangements has provided insights into the regulation of normal hematopoiesis and how disruption of key transcription factors and epigenetic modulators promote leukemic transformation. Cytogenetics has been widely adopted to provide the framework for development of risk-stratified treatment approaches to patient management.

Gene expression profiling in MDS and AML: potential and future avenues

Today, the classification systems for myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) already incorporate cytogenetic and molecular genetic aberrations in an attempt to better reflect disease biology. However, in many MDS/AML patients no genetic aberrations have been identified yet, and even within some cytogenetically well-defined subclasses there is considerable clinical heterogeneity. Recent advances in genomics technologies such as gene expression profiling (GEP) provide powerful tools to further characterize myeloid malignancies at the molecular level, with the goal to refine the MDS/AML classification system, incorporating as yet unknown molecular genetic and epigenetic pathomechanisms, which are likely reflected by aberrant gene expression patterns. In this study, we provide a comprehensive review on how GEP has contributed to a refined molecular taxonomy of MDS and AML with regard to diagnosis, prediction of clinical outcome, discovery of novel subclasses and identification of novel therapeutic targets and novel drugs. As many challenges remain ahead, we discuss the pitfalls of this technology and its potential including future integrative studies with other genomics technologies, which will continue to improve our understanding of malignant transformation in myeloid malignancies and thereby contribute to individualized risk-adapted treatment strategies for MDS and AML patients.