Deletion of MYC and presence of double minutes with MYC amplification in a morphologic acute promyelocytic leukemia–like case lacking RARA rearrangement: could early exclusion of double-minute chromosomes be a prognostic factor?

Molecular Heterogeneity of Pediatric AML with Atypical Promyelocytes Accumulation in Children—A Single Center Experience

Acute promyelocytic leukemia (APL) pathogenesis is based on RARA gene translocations, which are of high importance in the diagnosis of and proper therapy selection for APL. However, in some cases acute myeloid leukemia (AML) demonstrates APL-like morphological features such as atypical promyelocytes accumulation. This type of AML is characterized by the involvement of other RAR family members or completely different genes. In the present study, we used conventional karyotyping, FISH and high-throughput sequencing in a group of 271 de novo AML with atypical promyelocytes accumulation. Of those, 255 cases were shown to carry a typical chromosomal translocation t(15;17)(q24;q21) with PML::RARA chimeric gene formation (94.1%). Other RARA-positive cases exhibited cryptic PML::RARA fusion without t(15;17)(q24;q21) (1.8%, n = 5) and variant t(5;17)(q35;q21) translocation with NPM1::RARA chimeric gene formation (1.5%, n = 4). However, 7 RARA-negative AMLs with atypical promyelocytes accumulation were also discovered. These cases exhibited TBL1XR1::RARB and KMT2A::SEPT6 fusions as well as mutations, e.g., NPM1 insertion and non-recurrent chromosomal aberrations. Our findings demonstrate the genetic diversity of AML with APL-like morphological features, which is of high importance for successful therapy implementation.

Amazing roles of extrachromosomal DNA in cancer progression

In cancers, extrachromosomal DNA (ecDNA) has gained renewed interest since its first discovery, presenting its roles in tumorigenesis. Because of the unique structure and genetic characteristics, extrachromosomal DNA shed new light on development, early diagnosis, treatment and prognosis of cancers. Occurs in cancer cells, extrachromosomal DNA, one dissociative circular extrachromosomal element, drives the amplification of oncogenes, promotes the transcription and lifts tumor heterogeneity to participate in tumorigenesis. Given its role act as messenger, extrachromosomal DNA is connected with drug resistance, tumor microenvironment, germline and aging. The diversity of space and time gives extrachromosomal DNA a crucial role in cancer progression that has been ignored for decades. Thus, in this review, we will focus on some unique information of extrachromosomal DNA and the regulation of oncogenes as well as its roles and possible mechanisms in tumorigenesis, which are of great significance for us to understand extrachromosomal DNA comprehensively in carcinogenic mechanism.

MYC amplification in multiple marker chromosomes and EZH2 microdeletion in a man with acute myeloid leukemia

The role of MYC and EZH2 in acute myeloid leukemia (AML) pathogenesis is poorly understood. Herein we present a case of AML with MYC amplification in marker chromosomes and a microdeletion of chromosome 7 below cytogenetic resolution. The karyotype of the patient's bone marrow aspirate showed three to five marker chromosomes in all dividing cells without other structural or numerical chromosomal abnormalities. Analysis by fluorescence in situ hybridization (FISH) with a probe specific for the human MYC gene revealed amplification of the oncogene localized to the marker chromosomes. Using whole genome single nucleotide polymorphism (SNP) microarray analysis, an approximately 4.4 Mb amplicon containing the MYC gene was identified with an estimated amplification of about 30 copies per leukemic cell and, thus, an average of about 8 copies per marker chromosome. A 6.4 Mb hemizygous microdeletion of chromosome 7 within band q36.1 was also found by SNP microarray analysis in a cellular-equivalent dosage of 50%. The microdeletion spans multiple genes, including EZH2, a gene with well-known cancer association. No mutation was found in the remaining EZH2 allele by next generation gene sequencing. The combination of MYC amplification and EZH2 deletion, which has not been described previously in AML, may suggest a synergistic role of the two oncogenes in the pathogenesis of the patient's acute leukemia.

Genomic amplification of MYC as double minutes in a patient with APL-like leukemia

BACKGROUND

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML) characterized by a PML-RARA fusion due to a translocation t(15;17). Its sensitivity to treatment with all-trans retinoic acid (ATRA), which causes differentiation of the abnormal promyelocytes, combined with anthracycline based chemotherapy makes it the best curable subtype of acute myeloid leukemia. A rapid and accurate diagnosis is needed in the first place to prevent (more) bleeding problems. Here we present a patient with a leukemia with an APL-like morphology but no detectable PML-RARA fusion, as demonstrated by RT-PCR and cytogenetic analysis.

RESULTS

Unexpectedly, karyotyping revealed numerous double minutes (dmins). Fluorescence in situ hybridization (FISH) with DNA probes specific for the MYC-region showed the presence of multiple MYC amplicons. SNP-array analysis uncovered amplification of the 8q24.13-q24.21 region, including the MYC-gene, flanked by deletions in 8q24.13 and 8q24.21-q24.22, and a homozygous deletion in 9p21.3, flanked by heterozygous deletions in the same chromosome region.

CONCLUSIONS

The diagnosis was revised to AML, not otherwise specified (AML, NOS) and therefore therapy with ATRA was discontinued.

Concomitant and successive amplifications of MYC in APL-like leukemia

A 61-year-old male patient presented with very high blood white cell count, left shift of granulocytes to blasts, as well as low hemoglobin and platelets. The bone marrow aspirate and biopsy were consistent with an acute myeloid leukemia (AML). Blasts presented with large azurophilic inclusions and prominent Auer rods resembling acute promyelocytic leukemia (APL). Cytogenetic analysis revealed a deletion 9p and double-minute chromosomes. Fluorescence in situ hybridization showed amplification of the MYC probe and the absence of a RARA rearrangement. The patient achieved complete morphologic and cytogenetic remission 1 month after allogenic transplant, but relapsed 1 month later. Cytogenetics showed MYC amplification as a homogeneously staining region inserted into the long arm of one chromosome 9 and as a ring structure. At least five other acute promyelocytic leukemia-like cases without translocation 15;17, but with double minutes, have been reported in the literature. Only one of these had no RARA rearrangement. This report presents a second patient with APL-like bone marrow morphology, absence of RARA rearrangement, and MYC amplification. In this case, the amplification happened in various concomitant or successive forms.

Formation of non-random extrachromosomal elements during development, differentiation and oncogenesis

Extrachromosomal elements (EEs) were first discovered as minute chromatin bodies [Cox et al. Minute chromatin bodies in malignant tumors of childhood. Lancet 1965;62:55-8], and subsequently characterized as small circular DNA molecules physically separated from chromosomes. They include episomes, minichromosomes, small polydispersed DNAs or double minutes. This review focuses on eukaryotic EEs generated by genome rearrangements under physiological or pathological conditions. Some of those rearrangements occur randomly, but others are strictly non-random, highly regulated, and involve specific chromosomal locations (V(D)J-recombination, telomere maintenance mechanisms, c-myc deregulation). The multiple mechanisms of EEs formation are strongly interconnected and frequently linked to gene amplification. Identification of genes located on EEs will undoubtedly allow a better understanding of genome dynamics and oncogenic pathways.