The Prognosis of Karyotypic Subgroups in Pediatric Acute Myeloid Leukemia Depends on the Alterations of KIT, MLL and FLT3 Genes: A Report from Japanese Childhood AML Cooperative Study Group.

Karyotypic abnormalities are associated with a prognosis of acute myeloid leukemia (AML). However, there are some patients who had poor prognosis among patients with the same karyotypic abnormalities. Recently, it is revealed that alterations of the genes including tyrosine kinases, lead to poor prognosis in AML. Genetic alterations associated with a poor prognosis remain to be clarified in karytotypic subgroups of AML. We performed the mutation analysis of FLT3, MLL, KIT, RAS and NPM in 158 pediatric AML patients who were enrolled in Japanese Childhood AML Cooperative Treatment Protocol, AML99, including 33 with normal karyotype, 46 with t(8;21), 7 with inv(16), 20 with 11q23 translocations, 13 with t(15;17), 10 with Down syndrome (DS) FAB-M7 and 29 other karyotypic abnormalities. In the 33 patients with normal karyotype, 9 FLT3-internal tandem duplication (ITD), 2 FLT3-D835 mutation (D835Mt), 8 MLL-partial tandem duplication (PTD), 2 KIT, 2 NRAS and 3 KRAS mutations were identified. FLT3-ITD and MLL-PTD were associated with a poor prognosis. Notably, NPM gene mutation was not identified in these patients. In the 46 patients with t(8;21), 2 FLT3-ITD, 1 D835Mt, 4 MLL-PTD, 8 KIT, 4 NRAS and 5 KRAS mutations were found. KIT mutations were associated with a poor prognosis. In the 7 patients with inv(16), 2 FLT3-D835Mt and 1 KIT mutations were identified. Only one patient with KIT mutation relapsed. In the 20 patients with 11q23 translocations, 1 D835Mt and 5 MLL-PTD were identified. MLL-PTD was associated with a poor prognosis in patients with 11q23 translocations. In the 13 patients with t(15;17), 3 FLT3-ITD and 3 D835Mt were found. FLT3-ITD was not associated with a poor prognosis. In the 10 patients with DS-M7, KIT and KRAS mutations were found in each one patient, showing no prognostic significance. In the 29 patients with other karyotypic abnormalities, 6 FLT3-ITD, 2 D835Mt, 4 MLL-PTD, 0 KIT, 2 NRAS and 2 KRAS mutations were found. FLT3-ITD and MLL-PTD were associated with a poor prognosis. Fifteen patients (9.5%) who had alterations of 2 of these 4 genes showed a poor prognosis. RAS gene mutations were found in 26 (16.5%) of 158 patients, but were not associated with the prognosis. These results suggest that a new different therapeutic strategy for the patients with these gene alterations in each subgroup, for example KIT mutations in t(8;21)-patients and MLL-PTD in patients with 11q23 translocation, is needed to improve the prognosis of pediatric AML.