Incidence of ETV6 Cryptic Translocations In Myeloid Disorders

Abstract 2733

Rearrangements affecting band 12p13 are found as recurring chromosomal changes in myeloid malignancies. The main target of these rearrangements is the ETV6 gene, a member of the ETS family of transcription factors that is required for hematopoiesis within the bone marrow. To date, more than 41 translocations affecting ETV6 have been described, most of them encoding chimeric proteins with oncogenic properties. However, some of the translocations do not produce a functional fusion protein, but may induce ectopic expression of oncogenes located in the neighbourhood of the breakpoint.

In order to investigate the incidence of ETV6 aberrations in myeloid disorders and to search for novel ETV6 translocations, we performed fluorescence in situ hybridization (FISH) screening with a specific breakapart probe for the ETV6 gene (Abbott Vysis) on 134 acute myeloid leukemia (AML) cases, of which 20 cases were secondary AML evolved from myelodysplatic (MDS) or myeloproliferative syndromes (MPS), 10 MDS, and 3 MPS.

Conventional cytogenetic analysis of the cases identifed abnormal karyotypes in 72 cases, of which 20 cases presented del(12p), 5 cases add(12p), and 8 cases a translocation involving 12p. The remaining 39 abnormal karyotypes did not present alterations in the short arm of chromosome 12. Normal karyotypes were detected in 53 cases and cytogenetic analyses failed in 22 cases.

FISH detected 22 cases with heterozygous deletions of ETV6, of which 15 correlated with previous cytogenetic findings, 4 were detected in patients without evaluable mitoses, 2 were associated with add(12p), and one resulted from an unbalanced translocation involving chromosomes × and 12. In the remaining 7 translocations, FISH confirmed the t(3;12)/EVI1-ETV6, t(4;12)/CHIC2-ETV6, and t(5;12)/PDGFRβ-ETV6 in 4 cases, excluded an ETV6 involvement in 2 translocations, and revealed in one patient a novel t(3;12;17)(q21;p13;q25) with breakpoint in ETV6, previously described as t(3;12)(q21;p13).

Interestingly, cryptic translocations involving ETV6 were revealed in 3 patients with cytogenetically described 12p deletions: the t(12;17)(p13;p12–13) in a secondary AML¹; inv(12)(p13q24) in a secondary AML; and t(2;12)(p16.1;p13) in an AML FAB subtype M1.

In one additional patient with del(12p), FISH revealed a cryptic interstitial deletion with breakpoint in ETV6, del(12)(pterp13). In the latter patient, hybridization signals centromeric to ETV6 were deleted, whereas the probe hybridizing telomeric to ETV6 was retained on the derivative chromosome 12. Finally, one further ETV6 cryptic translocation, t(1;12)(p36;p13), was found in patient with MDS and an apparently normal karyotype.

The ETV6 translocation partner could be identified in the t(2;12)(p16.1;p13) and showed a novel fusion transcript derived from the ETV6 gene and the BAC clone RP11-440P5, on chromosome 2p16.1. DNA sequencing revealed an in-frame fusion of exon 7 of ETV6 to sequences derived from BAC 44OP5. We further investigated whether the ETV6 translocation partner in the t(1;12) was the recently described MDS2 gene of the t(1;12)(p36;p13).² However, RT-PCR with specific primers for ETV6 and MDS2 failed to amplified an ETV6-MDS2 fusion transcript. The molecular cloning of the inv(12) and the t(3;12;17) is in progress.

In conclusion, we have identified 6 new ETV6 rearrangements in patients with myeloid neoplasias, of which 5 were not seen by standard cytogenetic analyses. The prevalence of ETV6 rearrangements assessed by FISH (10/147, 6,8%) was 50% higher than by conventional cytogenetic (5/147, 3,4%). This study shows the relatively high frequency of cryptic translocations involving ETV6 on 12p13 and underlines the importance of FISH to detect and characterize these translocations.

This work was supported by the Deutsche José Carreras Leukämie-Stiftung eV.

References:

1. Murga Penas EM, Cools J, Algenstaedt P, et al. A novel cryptic translocation t(12;17)(p13;p12-p13) in a secondary acute myeloid leukemia results in a fusion of the ETV6 gene and the antisense strand of the PER1 gene. Genes Chromosomes Cancer. 2003;37(1):79–83.

2. Odero MD, Vizmanos JL, Román JP, et al. A novel gene, MDS2, is fused to ETV6/TEL in a t(1;12)(p36.1;p13) in a patient with myelodysplastic syndrome. Genes Chromosomes Cancer. 2002;35(1):11–19.