AML1-MTG8 generated by t(8;21)(q22;q22) contributes to leukemic transformation but additional events are required for full leukemogenesis. We examined whether mutations in the receptor tyrosine kinase (RTK) pathway could be the genetic events that cause acute myeloblastic leukemia (AML) harboring t(8;21). Mutations in the second tyrosine kinase domain, juxtamembrane domain and exon 8 of the C-KIT gene were observed in 7, 1 and 3 of 37 AML patients with t(8;21), respectively. Three patients showed an internal tandem duplication in the juxtamembrane domain of the FLT3 gene. One patient had a mutation in the K-Ras gene at codon 12. As the occurrence of these mutations was mutually exclusive, a total of 15 (41%) patients showed mutations in the RTK pathway. These results suggest that AML1-MTG8 predisposes cells to the acquisition of activating mutations in the RTK pathway as an additional event leading to the development of AML. Ten of 15 patients with mutations in the RTK pathway relapsed, compared with only 3 of 19 patients lacking such mutations (p=0.0042). Furthermore, the 6-year disease-free survival (DFS) in patients with mutations was 12% compared to 55% in those without mutations (p=0.0344). When patients who underwent allogeneic hematopoietic stem cell transplantation (HSCT) were censored at the date of the HSCT, patients with mutations had a 6-year DFS of 0% versus 60% for the patients without mutations (p=0.0096) These observations indicate that RTK mutations are associated with the clinical outcome in t(8;21) AML.

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