Heterogeneous patterns of FLT3 Asp(835) mutations in relapsed de novo acute myeloid leukemia: a comparative analysis of 120 paired diagnostic and relapse bone marrow samples.

We analyzed Asp(835) mutations of FLT3 on paired marrow samples at diagnosis and relapse from 120 adult patients with de novo acute myeloid leukemia (AML) to determine the role of FLT3 Asp(835) mutation in the relapse of AML. Asp(835) mutation was analyzed by DNA PCR amplification of exon 20 of FLT3 gene followed by EcoRV digestion. All of the mutations were confirmed by sequence analysis. Mutant to wild-type allelic ratio was determined by Genescan analysis. The Expand Long Template PCR System was used to determine the allelic location of internal tandem duplication of FLT3 (FLT3/ITD) and Asp(835) mutations. Thirteen patients had Asp(835) mutations at diagnosis, of them 8 lost the mutations at relapse, and the remaining 5 patients carrying Asp(835) mutations at diagnosis relapsed with the identical mutation types. Another 6 patients acquired Asp(835) mutations at relapse. Five samples harbored both FLT3/ITD and Asp(835) mutations that were found on different alleles by cloning analysis in the 3 patients studied. There were no differences in WBC count, French-American-British subtype, percentage of marrow blasts, or circulating blasts between patients with and without Asp(835) mutations, whereas the difference in the prevalence of Asp(835) mutations among cytogenetic/molecular subgroups was statistically significant (P = 0.025). The present study showed that patients with AML had heterogeneous patterns of FLT3 Asp(835) mutations, either acquisition or loss of the mutations at relapse. Asp(835) mutant clone may develop as a secondary event in a subset of patients with AML.