In acute myeloid leukemia (AML), further prognostic determinants are required in addition to cytogenetics to predict patients at increased risk of relapse. Recent studies have indicated that an internal tandem duplication (ITD) in the FLT3 gene may adversely affect clinical outcome. This study evaluated the impact of a FLT3/ITD mutation on outcome in 854 patients, mostly 60 years of age or younger, treated in the United Kingdom Medical Research Council (MRC) AML trials. An FLT3/ITD mutation was present in 27% of the patients and was associated with leukocytosis and a high percentage of bone marrow blast cells (P < .001 for both). It had a borderline association with a lower complete remission rate (P ‫؍‬ .05) and a higher induction death rate (P ‫؍‬ .04), and was associated with increased relapse risk (RR), adverse disease-free survival (DFS), event-free survival (EFS), and overall survival (OS) (P < .001 for all). In multivariate analysis, presence of a mutation was the most significant prognostic factor predicting RR and DFS (P < .0001) and was still significant for OS (P ‫؍‬ .009) and EFS (P ‫؍‬ .002). There was no evidence that the relative effect of a FLT3/ITD differed between the cytogenetic risk groups. More than one mutation was detected in 23% of FLT3/ITD ؉ patients and was associated with worse OS (P ‫؍‬ .04) and EFS (P ‫؍‬ .07

X-linked SCID (SCID-X1) is amenable to correction by gene therapy using conventional gammaretroviral vectors. Here, we describe the occurrence of clonal T cell acute lymphoblastic leukemia (T-ALL) promoted by insertional mutagenesis in a completed gene therapy trial of 10 SCID-X1 patients. Integration of the vector in an antisense orientation 35 kb upstream of the protooncogene LIM domain only 2 (LMO2) caused overexpression of LMO2 in the leukemic clone. However, leukemogenesis was likely precipitated by the acquisition of other genetic abnormalities unrelated to vector insertion, including a gain-of-function mutation in NOTCH1, deletion of the tumor suppressor gene locus cyclin-dependent kinase 2A (CDKN2A), and translocation of the TCR-β region to the STIL-TAL1 locus. These findings highlight a general toxicity of endogenous gammaretroviral enhancer elements and also identify a combinatorial process during leukemic evolution that will be important for risk stratification and for future protocol design.

BACKGROUNDDespite the molecular heterogeneity of standard-risk acute myeloid leukemia (AML), treatment decisions are based on a limited number of molecular genetic markers and morphology-based assessment of remission. Sensitive detection of a leukemia-specific marker (e.g., a mutation in the gene encoding nucleophosmin [NPM1]) could improve prognostication by identifying submicroscopic disease during remission. METHODSWe used a reverse-transcriptase quantitative polymerase-chain-reaction assay to detect minimal residual disease in 2569 samples obtained from 346 patients with NPM1-mutated AML who had undergone intensive treatment in the National Cancer Research Institute AML17 trial. We used a custom 51-gene panel to perform targeted sequencing of 223 samples obtained at the time of diagnosis and 49 samples obtained at the time of relapse. Mutations associated with preleukemic clones were tracked by means of digital polymerase chain reaction. RESULTSMolecular profiling highlighted the complexity of NPM1-mutated AML, with segregation of patients into more than 150 subgroups, thus precluding reliable outcome prediction. The determination of minimal-residual-disease status was more informative. Persistence of NPM1-mutated transcripts in blood was present in 15% of the patients after the second chemotherapy cycle and was associated with a greater risk of relapse after 3 years of follow-up than was an absence of such transcripts (82% vs. 30%; hazard ratio, 4.80; 95% confidence interval [CI], 2.95 to 7.80; P<0.001) and a lower rate of survival (24% vs. 75%; hazard ratio for death, 4.38; 95% CI, 2.57 to 7.47; P<0.001). The presence of minimal residual disease was the only independent prognostic factor for death in multivariate analysis (hazard ratio, 4.84; 95% CI, 2.57 to 9.15; P<0.001). These results were validated in an independent cohort. On sequential monitoring of minimal residual disease, relapse was reliably predicted by a rising level of NPM1-mutated transcripts. Although mutations associated with preleukemic clones remained detectable during ongoing remission after chemotherapy, NPM1 mutations were detected in 69 of 70 patients at the time of relapse and provided a better marker of disease status. CONCLUSIONSThe presence of minimal residual disease, as determined by quantitation of NPM1-mutated transcripts, provided powerful prognostic information independent of other risk factors.

An internal tandem duplication in the fms-like tyrosine kinase 3 gene (FLT3/ITD) is associated with poor prognosis in acute myeloid leukemia (AML), but the impact of mutant level, size, and interaction with nucleophosmin 1 (NPM1) mutations remains controversial. We evaluated these characteristics in a large cohort of young adult AML patients. There was a highly significant trend for worsening in relapse risk (RR) and overall survival (OS) with increasing FLT3/ITD mutant level (P < .001 for both), and even in the low level mutant group (1%-24% of total FLT3 alleles), RR was significantly worse than in the FLT3 wild-type (WT) group (P < .001). In multivariate analysis, mutant level was the most powerful prognostic factor for RR. Mutant size and number had no significant impact on outcome. The beneficial impact of an NPM1 mutation on RR and OS was seen in FLT3/ITD(+) as well as FLT3/WT patients; both markers were highly significant independent predictors of outcome (P < .001). Stratification using both markers identified 3 prognostic groups: good (FLT3/ITD(-)NPM1(+)), intermediate (FLT3/ITD(-)NPM1(-) or FLT3/ITD(+)NPM1(+)), and poor (FLT3/ITD(+)NPM1(-)). Patients with high FLT3/ITD mutant level (greater than 50%) or FLT3/ITD(+) in the absence of an NPM1 mutation may be good candidates for more experimental therapeutic approaches.