Impact of gemtuzumab ozogamicin on MRD and relapse risk in patients with NPM1-mutated AML: results from the AMLSG 09-09 trial.

Monitoring of measurable residual disease (MRD) provides prognostic information in patients with Nucleophosmin1-mutated (NPM1mut) acute myeloid leukemia (AML) and represents a powerful tool to evaluate treatment effects within clinical trials. We determined NPM1mut transcript levels (TLs) by quantitative reverse-transcription polymerase chain reaction and evaluated the prognostic impact of NPM1mut MRD and the effect of gemtuzumab ozogamicin (GO) on NPM1mut TLs and the cumulative incidence of relapse (CIR) in patients with NPM1mut AML enrolled in the randomized phase 3 AMLSG 09-09 trial. A total of 3733 bone marrow (BM) samples and 3793 peripheral blood (PB) samples from 469 patients were analyzed. NPM1mut TL log10 reduction ≥ 3 and achievement of MRD negativity in BM and PB were significantly associated with a lower CIR rate, after 2 treatment cycles and at end of treatment (EOT). In multivariate analyses, MRD positivity was consistently revealed to be a poor prognostic factor in BM and PB. With regard to treatment effect, the median NPM1mut TLs were significantly lower in the GO-Arm across all treatment cycles, resulting in a significantly greater proportion of patients achieving MRD negativity at EOT (56% vs 41%; P = .01). The better reduction in NPM1mut TLs after 2 treatment cycles in MRD positive patients by the addition of GO led to a significantly lower CIR rate (4-year CIR, 29.3% vs 45.7%, P = .009). In conclusion, the addition of GO to intensive chemotherapy in NPM1mut AML resulted in a significantly better reduction in NPM1mut TLs across all treatment cycles, leading to a significantly lower relapse rate.

Measurable residual disease monitoring in acute myeloid leukemia with t(8;21)(q22;q22.1): results from the AML Study Group.

We performed serial measurable residual disease (MRD) monitoring in bone marrow (BM) and peripheral blood (PB) samples of 155 intensively treated patients with RUNX1-RUNX1T1+ AML, using a qRT-PC-based assay with a sensitivity of up to 10-6. We assessed both reduction of RUNX1-RUNX1T1 transcript levels (TLs) and achievement of MRD negativity (MRD-) for impact on prognosis. Achievement of MR2.5 (>2.5 log reduction) after treatment cycle 1 and achievement of MR3.0 after treatment cycle 2 were significantly associated with a reduced risk of relapse (P = .034 and P = .028, respectively). After completion of therapy, achievement of MRD- in both BM and PB was an independent, favorable prognostic factor in cumulative incidence of relapse (4-year cumulative incidence relapse: BM, 17% vs 36%, P = .021; PB, 23% vs 55%, P = .001) and overall survival (4-year overall survival rate BM, 93% vs 70%, P = .007; PB, 87% vs 47%, P < .0001). Finally, during follow-up, serial qRT-PCR analyses allowed prediction of relapse in 77% of patients exceeding a cutoff value of 150 RUNX1-RUNX1T1 TLs in BM, and in 84% of patients exceeding a value of 50 RUNX1-RUNX1T1 TLs in PB. The KIT mutation was a significant factor predicting a lower CR rate and inferior outcome, but its prognostic impact was outweighed by RUNX1-RUNX1T1 TLs during treatment. Virtually all relapses occurred within 1 year after the end of treatment, with a very short latency from molecular to morphologic relapse, necessitating MRD assessment at short intervals during this time period. Based on our data, we propose a refined practical guideline for MRD assessment in RUNX1-RUNX1T1+ AML.

Secondary genetic lesions in acute myeloid leukemia with inv(16) or t(16;16): a study of the German-Austrian AML Study Group (AMLSG).

In this study, we evaluated the impact of secondary genetic lesions in acute myeloid leukemia (AML) with inv(16)(p13.1q22) or t(16;16)(p13.1;q22); CBFB-MYH11. We studied 176 patients, all enrolled on prospective treatment trials, for secondary chromosomal aberrations and mutations in N-/KRAS, KIT, FLT3, and JAK2 (V617F) genes. Most frequent chromosomal aberrations were trisomy 22 (18%) and trisomy 8 (16%). Overall, 84% of patients harbored at least 1 gene mutation, with RAS being affected in 53% (45% NRAS; 13% KRAS) of the cases, followed by KIT (37%) and FLT3 (17%; FLT3-TKD [14%], FLT3-ITD [5%]). None of the secondary genetic lesions influenced achievement of complete remission. In multivariable analyses, KIT mutation (hazard ratio [HR] = 1.67; P = .04], log(10)(WBC) (HR = 1.33; P = .02), and trisomy 22 (HR = 0.54; P = .08) were relevant factors for relapse-free survival; for overall survival, FLT3 mutation (HR = 2.56; P = .006), trisomy 22 (HR = 0.45; P = .07), trisomy 8 (HR = 2.26; P = .02), age (difference of 10 years, HR = 1.46; P = .01), and therapy-related AML (HR = 2.13; P = .14) revealed as prognostic factors. The adverse effects of KIT and FLT3 mutations were mainly attributed to exon 8 and tyrosine kinase domain mutations, respectively. Our large study emphasizes the impact of both secondary chromosomal aberrations as well as gene mutations for outcome in AML with inv(16)/t (16;16).

The value of allogeneic and autologous hematopoietic stem cell transplantation in prognostically favorable acute myeloid leukemia with double mutant CEBPA.

The clinical value of allogeneic hematopoietic stem cell transplantation (alloHSCT) and autologous hematopoietic stem cell transplantation (autoHSCT) in the subtype of acute myeloid leukemia (AML) with double mutant CEBPA (CEBPAdm) has remained unsettled. Among 2983 patients analyzed for CEBPA mutational status (age 18-60 years) treated on 4 published Dutch-Belgian-Swiss Hemato-Oncology Cooperative Group (HOVON/SAKK) and 3 German-Austrian AML Study Group (AMLSG) protocols (2 published, 1 registered, clinicaltrials.gov NCT00151255), 124 had AML with CEBPAdm and achieved first complete remission (CR1). Evaluation of the clinical impact of alloHSCT and autoHSCT vs chemotherapy was performed by addressing time dependency in the statistical analyses. Thirty-two patients proceeded to alloHSCT from a matched related (MRD, n = 29) or a matched unrelated donor (MUD, n = 3), 20 to autoHSCT in CR1 and 72 received chemotherapy. Relapse-free survival was significantly superior in patients receiving an alloHSCT or autoHSCT in CR1 as compared with chemotherapy (P < .001), whereas overall survival was not different (P < .12). Forty-five patients relapsed. Of 42 patients treated with reinduction therapy, 35 achieved a second CR (83%) and most patients (n = 33) received an alloHSCT MRD, n = 11; MUD, n = 19; haplo-identical donor, n = 3). Survival of relapsed patients measured from date of relapse was 46% after 3 years. Adult AML patients with CEBPAdm benefit from alloHSCT and autoHSCT; relapsed patients still have a favorable outcome after reinduction followed by alloHSCT.

Measurable Residual Disease Monitoring in AML With FLT3-ITD Treated With Intensive Chemotherapy Plus Midostaurin.

Measurable residual disease (MRD) monitoring in acute myeloid leukemia (AML) with FLT3 internal tandem duplication (FLT3-ITDpos) was hampered by the broad heterogeneity of ITD mutations. Using our recently developed FLT3-ITD paired-end next-generation sequencing (NGS)-based MRD assay with a limit of detection of 10-4 to 10-5, we evaluated the prognostic impact of MRD at different time-points in 157 FLT3-ITDpos AML patients enrolled in the AMLSG16-10 trial (NCT01477606) combining intensive chemotherapy with midostaurin followed by midostaurin maintenance. Achievement of MRD negativity (MRDneg) after two cycles of chemotherapy (Cy2) observed in 111/142 (78%) patients predicted for superior 4-year rates of cumulative incidence of relapse (CIR) (4y-CIR, 26% vs 46%; P=.001) and overall survival (OS) (4y-OS, 70% vs 44%; P=.012). This survival advantage was also seen for patients undergoing allogeneic hematopoietic-cell transplantation in first complete remission (4y-CIR, 14% vs 39%; P=.001; 4y-OS, 71% vs 49%; P=.029). Multivariate models for CIR and OS after Cy2 revealed FLT3-ITD MRDneg as the only consistent favorable variable for CIR (HR, 0.29; P=.006) and OS (HR, 0.39; P=.018). NPM1 co-mutation correlated with deeper molecular response as reflected by stronger MRD reduction and higher rate of FLT3-ITD MRDneg after Cy2. During follow-up, conversion from MRDneg to MRDpos was a strong, independent factor for inferior CIR (HR, 16.64; P<.001) and OS (HR, 4.05; P<.001). NGS-based FLT3-ITD MRD monitoring allows for the identification of patients at high risk of relapse and death following intensive chemotherapy plus midostaurin. Using NGS-based technology, FLT3-ITD emerges as a novel, clinically highly relevant target for MRD monitoring.

Prognostic impact, concurrent genetic mutations, and gene expression features of AML with CEBPA mutations in a cohort of 1182 cytogenetically normal AML patients: further evidence for CEBPA double mutant AML as a distinctive disease entity.

We evaluated concurrent gene mutations, clinical outcome, and gene expression signatures of CCAAT/enhancer binding protein alpha (CEBPA) double mutations (CEBPA(dm)) versus single mutations (CEBPA(sm)) in 1182 cytogenetically normal acute myeloid leukemia (AML) patients (16-60 years of age). We identified 151 (12.8%) patients with CEBPA mutations (91 CEBPA(dm) and 60 CEBPA(sm)). The incidence of germline mutations was 7% (5 of 71), including 3 C-terminal mutations. CEBPA(dm) patients had a lower frequency of concurrent mutations than CEBPA(sm) patients (P < .0001). Both, groups were associated with a favorable outcome compared with CEBPA(wt) (5-year overall survival [OS] 63% and 56% vs 39%; P < .0001 and P = .05, respectively). However, in multivariable analysis only CEBPA(dm) was a prognostic factor for favorable OS outcome (hazard ratio [HR] 0.36, P < .0001; event-free survival, HR 0.41, P < .0001; relapse-free survival, HR 0.55, P = .001). Outcome in CEBPA(sm) is dominated by concurrent NPM1 and/or FLT3 internal tandem duplication mutations. Unsupervised and supervised GEP analyses showed that CEBPA(dm) AML (n = 42), but not CEBPA(sm) AML (n = 18), expressed a unique gene signature. A 25-probe set prediction signature for CEBPA(dm) AML showed 100% sensitivity and specificity. Based on these findings, we propose that CEBPA(dm) should be clearly defined from CEBPA(sm) AML and considered as a separate entity in the classification of AML.

Mutations and treatment outcome in cytogenetically normal acute myeloid leukemia.

BACKGROUND: Mutations occur in several genes in cytogenetically normal acute myeloid leukemia (AML) cells: the nucleophosmin gene (NPM1), the fms-related tyrosine kinase 3 gene (FLT3), the CCAAT/enhancer binding protein alpha gene (CEPBA), the myeloid-lymphoid or mixed-lineage leukemia gene (MLL), and the neuroblastoma RAS viral oncogene homolog (NRAS). We evaluated the associations of these mutations with clinical outcomes in patients. METHODS: We compared the mutational status of the NPM1, FLT3, CEBPA, MLL, and NRAS genes in leukemia cells with the clinical outcome in 872 adults younger than 60 years of age with cytogenetically normal AML. Patients had been entered into one of four trials of therapy for AML. In each study, patients with an HLA-matched related donor were assigned to undergo stem-cell transplantation. RESULTS: A total of 53% of patients had NPM1 mutations, 31% had FLT3 internal tandem duplications (ITDs), 11% had FLT3 tyrosine kinase-domain mutations, 13% had CEBPA mutations, 7% had MLL partial tandem duplications (PTDs), and 13% had NRAS mutations. The overall complete-remission rate was 77%. The genotype of mutant NPM1 without FLT3-ITD, the mutant CEBPA genotype, and younger age were each significantly associated with complete remission. Of the 663 patients who received postremission therapy, 150 underwent hematopoietic stem-cell transplantation from an HLA-matched related donor. Significant associations were found between the risk of relapse or the risk of death during complete remission and the leukemia genotype of mutant NPM1 without FLT3-ITD (hazard ratio, 0.44; 95% confidence interval [CI], 0.32 to 0.61), the mutant CEBPA genotype (hazard ratio, 0.48; 95% CI, 0.30 to 0.75), and the MLL-PTD genotype (hazard ratio, 1.56; 95% CI, 1.00 to 2.43), as well as receipt of a transplant from an HLA-matched related donor (hazard ratio, 0.60; 95% CI, 0.44 to 0.82). The benefit of the transplant was limited to the subgroup of patients with the prognostically adverse genotype FLT3-ITD or the genotype consisting of wild-type NPM1 and CEBPA without FLT3-ITD. CONCLUSIONS: Genotypes defined by the mutational status of NPM1, FLT3, CEBPA, and MLL are associated with the outcome of treatment for patients with cytogenetically normal AML.

Prognostic impact of WT1 mutations in cytogenetically normal acute myeloid leukemia: a study of the German-Austrian AML Study Group.

To evaluate the incidence and clinical impact of WT1 gene mutations in younger adult patients with cytogenetically normal acute myeloid leukemia (CN-AML), sequencing of the complete coding region was performed in diagnostic samples from 617 patients who were treated on 3 German-Austrian AML Study Group protocols. WT1 mutations were identified in 78 (12.6%) of the 617 patients; mutations clustered in exon 7 (54 of 78) and exon 9 (13 of 78), but also occurred in exons 1, 2, 3, and 8. WT1 mutations were significantly associated with younger age, higher serum lactate dehydrogenase levels, higher blood blast counts, and the additional presence of FLT3-ITD (P < .001) and CEBPA mutations (P = .004). There was no difference in relapse-free survival and overall survival between patients with (WT1(mut)) or without WT1 mutations. Subset analysis showed that patients with the genotype WT1(mut)/FLT3-ITD(pos) had a lower complete remission rate (P = .003) and an inferior relapse-free survival (P = .006) and overall survival (P < .001) compared with those with the genotype WT1(mut)/FLT3-ITD(neg). In conclusion, in our large cohort of younger adults with CN-AML, WT1 mutation as a single molecular marker did not impact on outcome. However, our data suggest a negative impact of the genotype WT1(mut)/FLT3-ITD(pos).

Genomic heterogeneity in core-binding factor acute myeloid leukemia and its clinical implication.

Core-binding factor (CBF) acute myeloid leukemia (AML) encompasses AML with inv(16)(p13.1q22) and AML with t(8;21)(q22;q22.1). Despite sharing a common pathogenic mechanism involving rearrangements of the CBF transcriptional complex, there is growing evidence for considerable genotypic heterogeneity. We comprehensively characterized the mutational landscape of 350 adult CBF-AML [inv(16): n = 160, t(8;21): n = 190] performing targeted sequencing of 230 myeloid cancer-associated genes. Apart from common mutations in signaling genes, mainly NRAS, KIT, and FLT3, both CBF-AML entities demonstrated a remarkably diverse pattern with respect to the underlying cooperating molecular events, in particular in genes encoding for epigenetic modifiers and the cohesin complex. In addition, recurrent mutations in novel collaborating candidate genes such as SRCAP (5% overall) and DNM2 (6% of t(8;21) AML) were identified. Moreover, aberrations altering transcription and differentiation occurred at earlier leukemic stages and preceded mutations impairing proliferation. Lasso-penalized models revealed an inferior prognosis for t(8;21) AML, trisomy 8, as well as FLT3 and KIT exon 17 mutations, whereas NRAS and WT1 mutations conferred superior prognosis. Interestingly, clonal heterogeneity was associated with a favorable prognosis. When entering mutations by functional groups in the model, mutations in genes of the methylation group (ie, DNMT3A, TET2) had a strong negative prognostic impact.

Gene mutations and response to treatment with all-trans retinoic acid in elderly patients with acute myeloid leukemia. Results from the AMLSG Trial AML HD98B.

BACKGROUND: In a previous randomized trial, AML HD98B, we showed that administration of all-trans retinoic acid in addition to intensive chemotherapy improved the outcome of older patients with acute myeloid leukemia. The objectives of this study were to evaluate the prognostic impact of gene mutations and to identify predictive genetic factors for the all-trans retinoic acid treatment effect. DESIGN AND METHODS: Data from mutation analyses of the NPM1, CEBPA, FLT3, and MLL genes were correlated with outcome in patients 61 years and older treated within the AML HD98B trial. RESULTS: The frequencies of mutations were: NPM1, 23%; CEBPA, 8.5% (analysis restricted to patients with a normal karyotype); FLT3 internal tandem duplications (ITD), 17%; FLT3 tyrosine kinase domain mutations, 5%; and MLL partial tandem duplications, 4.5%. The genotype mutant NPM1 was positively and adverse cytogenetics as well as higher white blood cell count negatively correlated with achievement of complete remission. In Cox regression analysis, a significant interaction between the genotype mutant NPM1 without FLT3-ITD and treatment with all-trans retinoic acid was identified, in that the beneficial effect of all-trans retinoic acid on relapse-free and overall survival was restricted to this subgroup of patients. Other significant factors for survival were age, adverse cytogenetics, and logarithm of white cell count. CONCLUSIONS: In elderly patients with acute myeloid leukemia, NPM1 mutations are associated with achievement of complete remission, and the genotype 'mutant NPM1 without FLT3-ITD' appears to be a predictive marker for response to all-trans retinoic acid given as an adjunct to intensive chemotherapy (ClinicalTrials.gov Identifier: NCT00151242).

Clonal evolution patterns in acute myeloid leukemia with NPM1 mutation.

Mutations in the nucleophosmin 1 (NPM1) gene are considered founder mutations in the pathogenesis of acute myeloid leukemia (AML). To characterize the genetic composition of NPM1 mutated (NPM1mut) AML, we assess mutation status of five recurrently mutated oncogenes in 129 paired NPM1mut samples obtained at diagnosis and relapse. We find a substantial shift in the genetic pattern from diagnosis to relapse including NPM1mut loss (n = 11). To better understand these NPM1mut loss cases, we perform whole exome sequencing (WES) and RNA-Seq. At the time of relapse, NPM1mut loss patients (pts) feature distinct mutational patterns that share almost no somatic mutation with the corresponding diagnosis sample and impact different signaling pathways. In contrast, profiles of pts with persistent NPM1mut are reflected by a high overlap of mutations between diagnosis and relapse. Our findings confirm that relapse often originates from persistent leukemic clones, though NPM1mut loss cases suggest a second "de novo" or treatment-associated AML (tAML) as alternative cause of relapse.

JAK2V617F mutations as cooperative genetic lesions in t(8;21)-positive acute myeloid leukemia.

Significant progress has been made in identifying genetic lesions that are causally implicated in the pathogenesis of acute myeloid leukemia (AML). These insights improve our understanding of the genetic basis of the disease, a prerequisite for the development of novel therapeutic approaches.

RUNX1 mutations in acute myeloid leukemia: results from a comprehensive genetic and clinical analysis from the AML study group.

PURPOSE: To evaluate frequency, biologic features, and clinical relevance of RUNX1 mutations in acute myeloid leukemia (AML). PATIENTS AND METHODS: Diagnostic samples from 945 patients (age 18 to 60 years) were analyzed for RUNX1 mutations. In a subset of cases (n = 269), microarray gene expression analysis was performed. RESULTS: Fifty-nine RUNX1 mutations were identified in 53 (5.6%) of 945 cases, predominantly in exons 3 (n = 11), 4 (n = 10), and 8 (n = 23). RUNX1 mutations clustered in the intermediate-risk cytogenetic group (46 of 640, 7.2%; cytogenetically normal, 34 of 538, 6.3%), whereas they were less frequent in adverse-risk cytogenetics (five of 109, 4.6%) and absent in core-binding-factor AML (0 of 77) and acute promyelocytic leukemia (0 of 61). RUNX1 mutations were associated with MLL-partial tandem duplications (P = .0007) and IDH1/IDH2 mutations (P = .03), inversely correlated with NPM1 (P < .0001), and in trend with CEBPA (P = .10) mutations. RUNX1 mutations were characterized by a distinct gene expression pattern; this RUNX1 mutation-derived signature was not exclusive for the mutation, but also included mostly adverse-risk AML [eg, 7q-, -7, inv(3), or t(3;3)]. RUNX1 mutations predicted for resistance to chemotherapy (rates of refractory disease 30% and 19%, P = .047, for RUNX1-mutated and wild-type patients, respectively), as well as inferior event-free survival (EFS; P < .0001), relapse-free survival (RFS, P = .022), and overall survival (P = .051). In multivariable analysis, RUNX1 mutations were an independent prognostic marker for shorter EFS (P = .007). Explorative subgroup analysis revealed that allogeneic hematopoietic stem-cell transplantation had a favorable impact on RFS in RUNX1-mutated patients (P < .0001). CONCLUSION: AML with RUNX1 mutations are characterized by distinct genetic properties and are associated with resistance to therapy and inferior outcome.

Monitoring of minimal residual disease in NPM1-mutated acute myeloid leukemia: a study from the German-Austrian acute myeloid leukemia study group.

PURPOSE: To evaluate the prognostic value of minimal residual disease (MRD) in patients with acute myeloid leukemia (AML) with NPM1 mutation (NPM1(mut)). PATIENTS AND METHOD: RNA-based real-time quantitative polymerase chain reaction (RQ-PCR) specific for the detection of six different NPM1(mut) types was applied to 1,682 samples (bone marrow, n = 1,272; blood, n = 410) serially obtained from 245 intensively treated younger adult patients who were 16 to 60 years old. RESULTS: NPM1(mut) transcript levels as a continuous variable were significantly associated with prognosis after each treatment cycle. Achievement of RQ-PCR negativity after double induction therapy identified patients with a low cumulative incidence of relapse (CIR; 6.5% after 4 years) compared with RQ-PCR-positive patients (53.0%; P < .001); this translated into significant differences in overall survival (90% v 51%, respectively; P = .001). After completion of therapy, CIR was 15.7% in RQ-PCR-negative patients compared with 66.5% in RQ-PCR-positive patients (P < .001). Multivariable analyses after double induction and after completion of consolidation therapy revealed higher NPM1(mut) transcript levels as a significant factor for a higher risk of relapse and death. Serial post-treatment assessment of MRD allowed early detection of relapse in patients exceeding more than 200 NPM1(mut)/10(4) ABL copies. CONCLUSION: We defined clinically relevant time points for NPM1(mut) MRD assessment that allow for the identification of patients with AML who are at high risk of relapse. Monitoring of NPM1(mut) transcript levels should be incorporated in future clinical trials to guide therapeutic decisions.

Prognostic impact of minimal residual disease in CBFB-MYH11-positive acute myeloid leukemia.

PURPOSE: To evaluate the prognostic impact of minimal residual disease (MRD) in patients with acute myeloid leukemia (AML) expressing the CBFB-MYH11 fusion transcript. PATIENTS AND METHODS: Quantitative reverse transcriptase polymerase chain reaction (PCR) was performed on 684 bone marrow (BM; n = 331) and/or peripheral blood (PB; n = 353) samples (median, 13 samples per patient) from 53 younger adult (16 to 60 years old) patients with AML treated in prospective German-Austrian AML Study Group treatment trials. Samples were obtained at diagnosis (BM, n = 45; PB, n = 48), during treatment course (BM, n = 153; PB, n = 122), and at follow-up (BM, n = 133; PB, n = 183). To evaluate the applicability of PB for MRD detection, 198 paired BM and PB samples obtained at identical time points were analyzed. RESULTS: The following three clinically relevant checkpoints were identified during consolidation and early follow-up that predicted relapse: achievement of PCR negativity in at least one BM sample during consolidation therapy (2-year relapse-free survival [RFS], 79% v 54% for PCR positivity; P = .035); achievement of PCR negativity in at least two BM or PB samples during consolidation therapy and early follow-up (< or = 3 months; 2-year RFS, P = .001; overall survival, P = .01); and conversion from PCR negativity to PCR positivity with copy ratios of more than 10 after consolidation therapy. Analysis of paired BM and PB samples revealed BM samples to be more sensitive during the course of therapy, whereas for follow-up, PB samples were equally informative. CONCLUSION: We defined clinically relevant MRD checkpoints that allow for the identification of patients with CBFB-MYH11-positive AML who are at high risk of relapse. Monitoring of CBFB-MYH11 transcript levels should be incorporated into future clinical trials to guide therapeutic decisions.

Gene-expression profiling identifies distinct subclasses of core binding factor acute myeloid leukemia.

Core binding factor (CBF) leukemias, characterized by either inv(16)/t(16;16) or t(8;21), constitute acute myeloid leukemia (AML) subgroups with favorable prognosis. However, there exists substantial biologic and clinical heterogeneity within these cytogenetic groups that is not fully reflected by the current classification system. To improve the molecular characterization we profiled gene expression in a large series (n = 93) of AML patients with CBF leukemia [(inv (16), n = 55; t(8;21), n = 38)]. By unsupervised hierarchical clustering we were able to define a subgroup of CBF cases (n = 35) characterized by shorter overall survival times (P = .03). While there was no obvious correlation with fusion gene transcript levels, FLT3 tyrosine kinase domain, KIT, and NRAS mutations, the newly defined inv(16)/t(8;21) subgroup was associated with elevated white blood cell counts and FLT3 internal tandem duplications (P = .011 and P = .026, respectively). Supervised analyses of gene expression suggested alternative cooperating pathways leading to transformation. In the "favorable" CBF leukemias, antiapoptotic mechanisms and deregulated mTOR signaling and, in the newly defined "unfavorable" subgroup, aberrant MAPK signaling and chemotherapy-resistance mechanisms might play a role. While the leukemogenic relevance of these signatures remains to be validated, their existence nevertheless supports a prognostically relevant biologic basis for the heterogeneity observed in CBF leukemia.

Mutant nucleophosmin (NPM1) predicts favorable prognosis in younger adults with acute myeloid leukemia and normal cytogenetics: interaction with other gene mutations.

To assess the prognostic relevance of mutations in the NPM1 gene encoding a nucleocytoplasmic shuttle protein in younger adults with acute myeloid leukemia (AML) and normal cytogenetics, sequencing of NPM1 exon 12 was performed in diagnostic samples from 300 patients entered into 2 consecutive multicenter trials of the AML Study Group (AMLSG). Treatment included intensive double-induction therapy and consolidation therapy with high cumulative doses of high-dose cytarabine. NPM1 mutations were identified in 48% of the patients including 12 novel sequence variants, all leading to a frameshift in the C-terminus of the nucleophosmin 1 (NPM1) protein. Mutant NPM1 was associated with specific clinical, phenotypical, and genetic features. Statistical analysis revealed a significant interaction of NPM1 and FLT3 internal tandem duplications (ITDs). NPM1 mutations predicted for better response to induction therapy and for favorable overall survival (OS) only in the absence of FLT3 ITD. Multivariable analysis for OS revealed combined NPM1-mutated/FLT3 ITD-negative status, CEBPA mutation status, availability of a human leukocyte antigen (HLA)-compatible donor, secondary AML, and lactate dehydrogenase (LDH) as prognostic factors. In conclusion, NPM1 mutations in the absence of FLT3 ITD define a distinct molecular and prognostic subclass of young-adult AML patients with normal cytogenetics.