Late relapse of acute myeloid leukemia with mutated NPM1 after eight years: evidence of NPM1 mutation stability

The Role of Nucleophosmin 1 (NPM1) Mutation in the Diagnosis and Management of Myeloid Neoplasms

Nucleophosmin (NPM1) is a multifunctional protein with both proliferative and growth-suppressive roles in the cell. In humans, NPM1 is involved in tumorigenesis via chromosomal translocations, deletions, or mutation. Acute myeloid leukemia (AML) with mutated NPM1, a distinct diagnostic entity by the current WHO Classification of myeloid neoplasm, represents the most common diagnostic subtype in AML and is associated with a favorable prognosis. The persistence of NPM1 mutation in AML at relapse makes this mutation an ideal target for minimal measurable disease (MRD) detection. The clinical implication of this is far-reaching because NPM1-mutated AML is currently classified as being of standard risk, with the best treatment strategy (transplantation versus chemotherapy) yet undefined. Myeloid neoplasms with NPM1 mutations and <20% blasts are characterized by an aggressive clinical course and a rapid progression to AML. The pathological classification of these cases remains controversial. Future studies will determine whether NPM1 gene mutation may be sufficient for diagnosing NPM1-mutated AML independent of the blast count. This review aims to summarize the role of NPM1 in normal cells and in human cancer and discusses its current role in clinical management of AML and related myeloid neoplasms.

Nucleophosmin1 and isocitrate dehydrogenase 1 and 2 as measurable residual disease markers in acute myeloid leukemia

Monitoring measurable residual disease (MRD) in acute myeloid leukemia (AML) plays an important role in predicting relapse and outcome. The applicability of the leukemia-initiating nucleophosmin1 (NPM1) gene mutations in MRD detection is well-established, while that of isocitrate dehydrogenase1/2 (IDH1/2) mutations are matter of debate. The aim of this study was to investigate the stability of NPM1 and IDH1/2 mutations at diagnosis and relapse retrospectively in 916 adult AML patients. The prognostic value of MRD was evaluated by droplet digital PCR on the DNA level in a selected subgroup of patients in remission. NPM1 re-emerged at relapse in 91% (72/79), while IDH1/2 in 87% (20/23) of mutation-positive cases at diagnosis. NPM1 mutation did not develop at relapse, on the contrary novel IDH1/2 mutations occurred in 3% (3/93) of previously mutation-negative cases. NPM1 MRD-positivity after induction (n = 116) proved to be an independent, adverse risk factor (MRD^pos 24-month OS: 39.3±6.2% versus MRD^neg: 58.5±7.5%, p = 0.029; HR: 2.16; 95%CI: 1.25–3.74, p = 0.006). In the favorable subgroup of mutated NPM1 without fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) or with low allelic ratio, NPM1 MRD provides a valuable prognostic biomarker (NPM1 MRD^pos versus MRD^neg 24-month OS: 42.9±6.7% versus 66.7±8.6%; p = 0.01). IDH1/2 MRD-positivity after induction (n = 62) was also associated with poor survival (MRD^pos 24-month OS: 41.3±9.2% versus MRD^neg: 62.5±9.0%, p = 0.003; HR 2.81 95%CI 1.09–7.23, p = 0.032). While NPM1 variant allele frequency decreased below 2.5% in remission in all patients, IDH1/2 mutations (typically IDH2 R140Q) persisted in 24% of cases. Our results support that NPM1 MRD even at DNA level is a reliable prognostic factor, while IDH1/2 mutations may represent pre-leukemic, founder or subclonal drivers.

Nucleophosmin1 (NPM1) abnormality in hematologic malignancies, and therapeutic targeting of mutant NPM1 in acute myeloid leukemia

Nucleophosmin (NPM1) is an abundant nucleolar protein that is implicated in a variety of biological processes and in the pathogenesis of several human malignancies. For hematologic malignancies, approximately one-third of anaplastic large-cell non-Hodgkin’s lymphomas were found to express a fusion between NPM1 and the catalytic domain of anaplastic lymphoma receptor tyrosine kinase. About 50–60% of acute myeloid leukemia patients with normal karyotype carry NPM1 mutations, which are characterized by cytoplasmic dislocation of the NPM1 protein. Nevertheless, NPM1 is overexpressed in various hematologic and solid tumor malignancies. NPM1 overexpression is considered a prognostic marker of recurrence and progression of cancer. Thus, NPM1 abnormalities play a critical role in several types of hematologic malignancies. This has led to intense interest in the development of an NPM1 targeting strategy for cancer therapy. The aim of this review is to summarize present knowledge on NPM1 origin, pathogenesis, and therapeutic interventions in hematologic malignancies.

Minimal/Measurable Residual Disease Monitoring in NPM1-Mutated Acute Myeloid Leukemia: A Clinical Viewpoint and Perspectives

Acute myeloid leukemia (AML) with NPM1 gene mutations is currently recognized as a distinct entity, due to its unique biological and clinical features. We summarize here the results of published studies investigating the clinical application of minimal/measurable residual disease (MRD) in patients with NPM1-mutated AML, receiving either intensive chemotherapy or hematopoietic stem cell transplantation. Several clinical trials have so far demonstrated a significant independent prognostic impact of molecular MRD monitoring in NPM1-mutated AML and, accordingly, the Consensus Document from the European Leukemia Net MRD Working Party has recently recommended that NPM1-mutated AML patients have MRD assessment at informative clinical timepoints during treatment and follow-up. However, several controversies remain, mainly with regard to the most clinically significant timepoints and the MRD thresholds to be considered, but also with respect to the optimal source to be analyzed, namely bone marrow or peripheral blood samples, and the correlation of MRD with other known prognostic indicators. Moreover, we discuss potential advantages, as well as drawbacks, of newer molecular technologies such as digital droplet PCR and next-generation sequencing in comparison to conventional RQ-PCR to quantify NPM1-mutated MRD. In conclusion, further prospective clinical trials are warranted to standardize MRD monitoring strategies and to optimize MRD-guided therapeutic interventions in NPM1-mutated AML patients.

Minimal Residual Disease Monitoring of Acute Myeloid Leukemia by Massively Multiplex Digital PCR in Patients with NPM1 Mutations

The presence of minimal residual disease (MRD) is widely recognized as a powerful predictor of therapeutic outcome in acute myeloid leukemia (AML), but methods of measurement and quantification of MRD in AML are not yet standardized in clinical practice. There is an urgent, unmet need for robust and sensitive assays that can be readily adopted as real-time tools for disease monitoring. NPM1 frameshift mutations are an established MRD marker present in half of patients with cytogenetically normal AML. However, detection is complicated by the existence of hundreds of potential frameshift insertions, clonal heterogeneity, and absence of sequence information when the NPM1 mutation is identified using capillary electrophoresis. Thus, some patients are ineligible for NPM1 MRD monitoring. Furthermore, a subset of patients with NPM1-mutated AML will have false-negative MRD results because of clonal evolution. To simplify and improve MRD testing for NPM1, we present a novel digital PCR technique composed of massively multiplex pools of insertion-specific primers that selectively detect mutated but not wild-type NPM1. By measuring reaction end points using digital PCR technology, the resulting single assay enables sensitive and specific quantification of most NPM1 exon 12 mutations in a manner that is robust to clonal heterogeneity, does not require NPM1 sequence information, and obviates the need for maintenance of hundreds of type-specific assays and associated plasmid standards.

Examination of the FLT3 and NPM1 mutational status in patients with acute myeloid leukemia from southeastern Poland

INTRODUCTION

Acute myeloid leukemia (AML) is a genetically heterogeneous disease at both the cytogenetic and molecular levels. In AML cells many chromosomal aberrations are observed, some of them being characteristic of a particular subtype of patients, and others being less significant. Besides chromosomal abnormalities, the leukemic cells can have a variety of mutations involving individual genes. The aim of this work was to investigate the frequencies of molecular alterations with the focus on FLT3-ITD and NPM1 mutations in AML patients of different age groups living in a southeastern region of Poland.

MATERIAL AND METHODS

The study group comprised 50 consecutive AML patients. We analyzed bone marrow samples by conventional cytogenetics. Cytogenetic evaluation in selected cases was complemented by the FISH technique. The internal tandem mutation in the FLT3 gene was identified using polymerase chain reaction (PCR), and the NPM1 mutation was assessed by direct nucleotide sequencing.

RESULTS

The studies using classical cytogenetics showed chromosomal aberrations in 32 (64%) patients. In 18 cases no changes in the karyotype were found by conventional karyotyping. FLT3-ITD mutation was detected in 4 (8%) patients and mutation of NPM1 in 3 patients with AML (6%).

CONCLUSIONS

The incidence of both mutations in our study group was lower than described elsewhere. We have confirmed that FLT3-ITD occurred more commonly in older patients and it was associated with shorter overall survival. By contrast, mutation of exon 12 of the NPM1 gene seems to be a good prognostic factor in AML patients with normal karyotype.

Quantitative detection of circulating nucleophosmin mutations DNA in the plasma of patients with acute myeloid leukemia

OBJECTIVE

The aim of this study was to quantify the copies of circulating nucleophosmin (NPM) mutations DNA in the plasma of patients with acute myeloid leukemia (AML) and to explore the association of circulating NPM mutation levels with clinical characteristics.

DESIGN AND METHODS

The presence of NPM mutations in 100 Chinese patients newly diagnosed with AML were identified by RT-PCR and sequencing analysis. Copies of circulating NPM mutation A (NPM mut.A) DNA in the plasma of mutation-positive cases were quantified by real-time quantitative PCR (qRT-PCR). Furthermore, the association of circulating NPM mutation levels and clinical characteristics was analyzed.

RESULTS

NPM mutations were identified in 37 of the 100 patients and all cases were NPM mut.A. The circulating NPM mut.A levels ranged from 0.35×10(8) copies/ml to 6.0×10(8) copies/ml in the 37 mutation-positive cases. The medium and quartile M (P25, P75) of the circulating NPM mut.A levels in patients classified as M2, M4 and M5 morphological subtypes were 1.35×10(8) (0.76×10(8), 1.91×10(8)) copies/ml, 1.81×10(8) (1.47×10(8), 2.2×10(8)) copies/ml and 2.50×10(8) (2.42×10(8), 3.05×10(8)) copies/ml, respectively. Circulating NPM mut.A levels were significantly higher in patients with the M5 subtype of AML compared to patients with the M2 and M4 subtypes (p=0.000, p=0.046). In addition, circulating NPM mut.A copies were significantly associated with a higher white blood cell count, platelet count and bone marrow blast percentage (p<0.05).

CONCLUSION

Our results suggest that circulating NPM mutations DNA assay serves as a complementary to the routine investigative protocol of NPM-mutated leukemia.

Is acute myeloid leukemia a liquid tumor?

Extramedullary manifestations of acute myeloid leukemia (AML) were described as early as the 19th century. However, the incidence, clinical significance and pathobiology of extramedullary AML remain ill defined. We reviewed case reports, retrospective case series, pilot studies and imaging studies of extramedullary leukemia (EML) to determine its frequency, characteristics, clinical presentation and significance. EML precedes or accompanies development of AML and occurs during or following treatment, even during remission. Although imaging studies are rarely conducted and the true incidence of EML has yet to be verified, authors have reported several estimates based on retrospective and autopsy studies. The incidence of EML in patients with AML of all ages is estimated to be about 9% and EML in children with AML was detected in 40% of patients at diagnosis. The combination of positron emission tomography and computed tomography were the most sensitive and reliable techniques of detecting and monitoring EML. Based on our literature review, the frequency of EML is likely underreported. The well-documented nature of EML in patients with AML suggests that AML can manifest as a solid tumor. The extent to which EML accompanies AML and whether EML is derived from bone marrow are unknown. Furthermore, questions remain regarding the role of the microenvironment, which may or may not facilitate the survival and proliferation of EML, and the implications of these interactions with regard to minimal residual disease, tumor cell quiescence and relapse. Therefore, prospective studies of detection and characterization of EML in patients with AML are warranted.