Use of Sorafenib as an effective treatment in an AML patient carrying a new point mutation affecting the Juxtamembrane domain of FLT3

Point Mutations in the FLT3-ITD Region Are Rare but Recurrent Alterations in Adult AML and Associated With Concomitant KMT2A-PTD

FLT3-ITD mutations are common druggable alterations in patients with acute myeloid leukemia (AML) and associated with poor prognosis. Beside typical ITD mutations, point mutations and deletions in the juxtamembrane domain (JMD) have been observed. However, due to the low frequency of these alterations, there is only limited information on molecular and clinical associations. To evaluate the prognostic impact of non-ITD mutations in the FLT3 JMD region, we analyzed a large cohort of 1,539 adult AML patients treated in different protocols of the Study Alliance Leukemia, using next-generation sequencing. Non-ITD point mutations and deletions within the FLT3 JMD were identified with a prevalence of ~1.23% (n = 19). Both FLT3-ITD and non-ITD mutations were associated with a higher rate of NPM1 (42%-61%; p < 0.001) and DNMT3A mutations (37%-43%; p < 0.001), as well as an increased percentage of peripheral blood (54%-65%) and bone marrow blast cells (74%; p < 0.001), compared to FLT3-wild-type patients. Most significantly, AML patients with FLT3 non-ITD mutations had a higher rate of concomitant KMT2A-PTD mutations (37.5%; p < 0.001) as compared to FLT3-ITD (7%) or FLT3-wild-type cases (4.5%). In a multivariable analysis, FLT3 non-ITD mutations were not an independent prognostic factor. However, patients with dual FLT3 non-ITD and KMT2A-PTD mutations showed a trend for inferior outcome, which points at a functional interaction in this subset of AML.

Analysis for loss of heterozygosity on chromosome arm 13q by STR analysis or SNP sequencing can replace analysis of FLT3-ITD to detect patients with prognostically adverse AML

We aimed at developing novel assays for Loss of Heterozygosity (LOH) detection on 13q as a substitute for FLT3-ITD analysis to identify acute myeloid leukemia (AML) patients with high risk of shorter survival. To this aim, we first analyzed a selected cohort of 185 patients with (n = 138) or without (n = 47) FLT3-ITD by short tandem repeat (STR) analysis for 13q LOH. In 46 of 138 FLT3-ITD positive cases, a FLT3-ITD/FLT3wt ratio of ≥ 1 was measured indicating LOH. Applying analysis with a combination of five different STR markers, a threshold of an STR allelic ratio of >65% allows the identification of LOH in 40/46 (87%) samples. Survival analysis revealed significantly inferior outcome in patients with LOH as detected by STR analysis (event free survival (EFS): no LOH: 13.3 months versus LOH: 4.5 months, p < 0.001; overall survival (OS): no LOH: 35.8 months versus LOH: 9.7 months, p = 0.001). In multivariate Cox regression analysis, 13q LOH was found to be an independent adverse parameter for EFS and OS (p = 0.003 and p < 0.001, respectively) besides age and white blood cell count. Thus, the prognostic impact of 13q LOH is nearly identical to the one of FLT3-ITD/FLT3wt load of ≥ 1 and thus is a feasible alternative to identify respective patients with high risk AML. In a second approach, a cohort of 91 patients was subjected to a proof-of-principle study of applying single nucleotide polymorphism analysis by next generation amplicon sequencing for detection of LOH. 53/91 cases had LOH and 50 were identified with this new method resulting in a positive detection rate of 94.3%.

Allogeneic stem cell transplantation and targeted therapy for FLT3/ITD+ acute myeloid leukemia: an update

Survival of patients with acute myelogenous leukemia (AML), particularly in younger patients, has improved in recent years due to improved understanding of disease biology, post remission therapies and supportive care. AML, however, remains difficult to treat as many patients will still ultimately relapse and die of their disease. This is particularly true in AML patients with identified FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) molecular mutations, which typically confers a poor prognosis. The FLT3-ITD mutation occurs in about one-quarter of patients diagnosed with AML. Oftentimes, these patients are referred for early allogeneic hematopoietic stem cell transplantation (HSCT) in hopes of overcoming this poor prognostic factor. Several studies have demonstrated some benefit with HSCT in patients with FLT3-ITD mutation. However, recent data suggested that FLT3-ITD mutation remains a poor prognostic factor even after early HSCT; these patients remain at risk for early relapse after transplantation, emphasizing ongoing efforts to explore maintenance therapy with FLT3-ITD inhibitors in the post-transplant setting.