Therapy-related myeloproliferative neoplasm with ETV6-PDGFRB rearrangement following treatment of acute promyelocytic leukemia

Marked response to imatinib mesylate in a patient with platelet-derived growth factor receptor beta-associated acute myeloid leukemia

Abnormal platelet-derived growth factor receptor (PDGFR)-mediated signaling may cause hematologic neoplasm. The PDGFR beta (PDGFRB) gene, located at chromosome band 5q31-33, forms a fusion gene as a result of chromosome translocation. Although patients with PDGFRB rearrangement mostly present with myeloproliferative neoplasm and eosinophilia, acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) have also been reported in this population. Treatment with imatinib mesylate alone has been shown to have excellent long-term efficacy against myeloproliferative neoplasms; however, its long-term effects on ALL and AML have not been elucidated. A 75-year-old man was diagnosed with acute myeloid leukemia having the PDGFRB and cGMP-dependent protein kinase 2 fusion gene with additional genetic abnormalities. Continuous therapy with single-agent imatinib mesylate resulted in cytogenetic remission and decreased molecular burden for 9 months; however, the leukemia subsequently recurred, and the patient died 1 year after initiation of treatment. This case report supports the importance of cytogenetic analysis during patient screening.

TRIP11-PDGFRB fusion in a patient with a therapy-related myeloid neoplasm with t(5;14)(q33;q32) after treatment for acute promyelocytic leukemia

Background

Therapy-related myeloid neoplasm after treatment for acute promyelocytic leukemia (APL) is a relatively infrequent but severe complication. Most therapy-related myeloid neoplasms after treatment for APL are classified as therapy-related myelodysplastic syndrome or therapy-related acute myeloid leukemia. Translocation of 5q31-33, PDGFRB occur rarely in therapy-related myeloid neoplasm and there has been two identified PDGFRB partner genes located at 14q32, TRIP11 and KIAA1509.

Results

The TRIP11-PDGFRB fusion was identified in a patient with therapy-related myeloid neoplasm with t(5;14)(q33;q32) after treatment of APL using conventional cytogenetics, fluorescence in situ hybridization (FISH) and molecular methods. Cytogenetic analysis of the bone marrow aspirate revealed 46, XY, t(5;14)(q33;q32) in all 20 analyzed cells. No other cytogenetic abnormalities were observed. Break-apart FISH analysis demonstrated that rearrangement of PDGFRB at 5q33 was positive in 460 of 500 cells analyzed, while the PML-RARA rearrangement remained undetectable by RT-PCR. Sequencing of RT-PCR products revealed fusion between exon 16 of TRIP11 and exon 11 of PDGFRB. However, the KIAA1509-PDGFRB fusion was not detected by RT-PCR.

Conclusion

We firstly demonstrated that therapy-related myeloid neoplasm with TRIP11-PDGFRB fusion was identified after treatment of APL.

ETV6 fusion genes in hematological malignancies: a review

Translocations involving band 12p13 are one of the most commonly observed chromosomal abnormalities in human leukemia and myelodysplastic syndrome. Their frequently result in rearrangements of the ETV6 gene. At present, 48 chromosomal bands have been identified to be involved in ETV6 translocations, insertions or inversions and 30 ETV6 partner genes have been molecularly characterized. The ETV6 protein contains two major domains, the HLH (helix-loop-helix) domain, encoded by exons 3 and 4, and the ETS domain, encoded by exons 6 through 8, with in between the internal domain encoded by exon 5. ETV6 is a strong transcriptional repressor, acting through its HLH and internal domains. Five potential mechanisms of ETV6-mediated leukemogenesis have been identified: constitutive activation of the kinase activity of the partner protein, modification of the original functions of a transcription factor, loss of function of the fusion gene, affecting ETV6 and the partner gene, activation of a proto-oncogene in the vicinity of a chromosomal translocation and dominant negative effect of the fusion protein over transcriptional repression mediated by wild-type ETV6. It is likely that ETV6 is frequently involved in leukemogenesis because of the large number of partners with which it can rearrange and the several pathogenic mechanisms by which it can lead to cell transformation.