Prognostic factors in children with acute myeloid leukaemia and excellent response to remission induction therapy

Minimal residual disease (MRD) is a strong prognostic factor in children and adolescents with acute myeloid leukaemia (AML) but nearly one‐quarter of patients who achieve MRD‐negative status still relapse. The adverse prognostic factors among MRD‐negative patients remain unknown. We analysed the AML02 study cohort to identify demographic and genetic prognostic factors. Among the presenting features, certain 11q23 abnormalities, such as t(6;11) and t(10;11), acute megakaryoblastic leukaemia without the t(1;22), and age ≥10 years were associated with inferior outcome in patients who had MRD‐negative status after either remission induction I or II. By contrast, those with rearrangement of CBF genes had superior outcome. Our study identifies patient populations for whom close post‐remission MRD monitoring to detect and treat emerging relapse and adjustment in treatment intensity might be indicated.     

Early immunophenotypical evaluation of minimal residual disease in acute myeloid leukemia identifies different patient risk groups and may contribute to postinduction treatment stratification

Early response to therapy is one of the most important prognostic factors in acute leukemia. It is hypothesized that early immunophenotypical evaluation may help identify patients at high risk for relapse from those who may remain in complete remission (CR). Using multiparametric flow cytometry, the level of minimal residual disease (MRD) was evaluated in the first bone marrow (BM) in morphologic CR obtained after induction treatment from 126 patients with acute myeloid leukemia (AML) who displayed aberrant phenotypes at diagnosis. Based on MRD level, 4 different risk categories were identified: 8 patients were at very low risk (fewer than 10(-4) cells), and none have relapsed thus far; 37 were at low risk (10(-4) to 10(-3) cells); and 64 were at intermediate risk (fewer than 10(-3) to 10(-2) cells), with 3-year cumulative relapse rates of 14% and 50%, respectively. The remaining 17 patients were in the high-risk group (more than 10(-2) residual aberrant cells) and had a 3-year relapse rate of 84% (P =.0001). MRD level not only influences relapse-free survival but also overall survival (P =.003). The adverse prognostic impact was also observed when M3 and non-M3 patients with AML were separately analyzed, and was associated with adverse cytogenetic subtypes, 2 or more cycles to achieve CR, and high white blood cell counts. Multivariate analysis showed that MRD level was the most powerful independent prognostic factor, followed by cytogenetics and number of cycles to achieve CR. In conclusion, immunophenotypical investigation of MRD in the first BM in mCR obtained after AML induction therapy provides important information for risk assessment in patients with AML.     

Clinical significance of minimal residual disease in childhood acute myeloid leukemia

Many studies have assessed the clinical significance of the detection of minimal residual disease (MRD) in acute leukemia. Thus far, many studies have suggested that MRD detection to evaluate the response to chemotherapy is useful for predicting the prognosis of childhood acute lymphoblastic leukemia (ALL). However, few studies have reported on the significance of MRD in childhood acute myeloid leukemia (AML), because of small numbers of patients and limited availability of MRD markers. Therefore, we monitored MRD using currently available markers at several points during the treatment for childhood AML and tried to intensify the treatment based on the results of MRD. Thirty-one patients (26 de novo cases and 5 other cases) were examined for MRD between February 1999 and May 2002. After the first consolidation therapy (consolidation 1), the expression of Wilms tumor gene (WT1) and/or leukemia-specific fusion genes such as AML1/MTG8, PML/RAR alpha, and MYH11/CBF beta were analyzed. Patients with positive MRD but in hematological remission at that point were recommended to undergo stem cell transplantation (SCT). Positive WT1 expression (more than 10(3) copies/microgram RNA) was detected in 18 of 31 patients (58.1%) at onset. After consolidation 1 therapy, the WT1 expression became negative in 14 of 18 patients. The AML1/MTG8 fusion gene was expressed in 8 patients, PML/RAR alpha was expressed in 3 patients, and MYH11/CBF beta was expressed in 1 patient. Four of the 8 patients with AML1/MTG8 expression and all 3 with PML/RAR alpha expression also demonstrated positive WT1 expression at onset. Eight (5 de novo cases and 3 other cases) of the 31 patients had no available MRD markers. Four patients who showed pesistently high expression of WT1 after consolidation 1 therapy underwent SCT, and only 1 patient remained in complete remission (CR). Among 14 patients who became negative for WT1 expression, 6 patients received SCT for various reasons. Among 8 patients with the AML1/MTG8 fusion gene, 2 became MRD negative and 6 continued to be positive. Four of these 6 patients underwent SCT, and all but one who underwent syngeneic SCT became MRD negative. On the other hand, 1 of the 2 patients who continued on chemotherapy continued to be MRD positive, suggesting a graft-versus-leukemia effect in allogeneic SCT. All patients with the PML/RAR alpha and MYH11/CBF beta fusion gene continued to be in CR. The 3-year event-free survival in de novo AML was 69.4% +/- 9.8% (n = 26), a result that is encouraging and superior to other reported outcomes. Thus, an MRD-based treatment strategy together with conventional risk factors appears to be required for further improving the outcomes of AML.     

Level of minimal residual disease after consolidation therapy predicts outcome in acute myeloid leukemia

We used flow cytometry to quantify minimal residual disease (MRD) in 56 patients with acute myeloid leukemia (AML) expressing a leukemia-associated phenotype. Thirty-four patients aged 18 to 60 years were entered into the AML-10 protocol (induction, consolidation, and autologous stem-cell transplantation [ASCT]), whereas 22 patients older than 60 years received the AML-13 protocol (induction, consolidation, and consolidation II). After induction, the level of MRD that was best associated with treatment outcome was 4.5 x 10(-4) residual leukemic cells. However, the outcome in patients with at least 4.5 x 10(-4) cells (n = 26) was not significantly different from that in patients with fewer leukemic cells (n = 30); there were 15 (58%) relapses in the first group and 12 (40%) relapses in the second. After consolidation, the most predictive MRD cutoff value was 3.5 x 10(-4) cells: 22 patients had an MRD level of 3.5 x 10(-4) cells or higher and 17 (77%) of these patients had relapse, compared with 5 of 29 patients (17%) with lower MRD levels (P <.001). An MRD level of 3.5 x 10(-4) cells or higher after consolidation was significantly correlated with poor or intermediate-risk cytogenetic findings, a multidrug resistance 1 (MDR1) phenotype, short duration of overall survival, and short duration of relapse-free survival (P =.014,.031,.00022, and.00014, respectively). In multivariate analysis, this MRD status was significantly associated with a high frequency of relapse (P <.001) and a short duration of overall (P =.025) and relapse-free survival (P =.007). ASCT did not alter the prognostic effect of high MRD levels after consolidation: the relapse rate after transplantation was 70%. Thus, we found that an MRD level of 3.5 x 10(-4) cells or higher at the end of consolidation strongly predicts relapse and is significantly associated with an MDR1 phenotype and intermediate or unfavorable cytogenetic findings. (Blood. 2000;96:3948-3952)     

Durable remissions with venetoclax monotherapy in secondary AML refractory to hypomethylating agents and high expression of BCL‐2 and/or BIM

Acute myeloid leukemia (AML) is a disease of the elderly population and survival remains poor after failure of hypomethylating agents (HMA). The BCL‐2 inhibitor venetoclax demonstrated activity as monotherapy and in combination with chemotherapy or HMA in AML. In this case series, patients with secondary AML (sAML) not eligible for intensive chemotherapy and refractory to HMA were treated with venetoclax within a named patient program at our tertiary cancer center in Salzburg, Austria. Between April 2017 and September 2018, seven patients with sAML received venetoclax therapy. Two out of seven patients achieved a complete remission upon venetoclax initiation with a PFS of 505 days and 352 days and another patient achieved complete peripheral blood blast clearing within nine days after start of venetoclax. Among the venetoclax responders, primary refractory disease to prior HMA therapy was documented, 2 patients harbored IDH1/IDH2 mutations and one patient had an antecedent myeloproliferative neoplasm. High BCL‐2 and/or BIM expression in myeloblasts was found in venetoclax responders and response was significantly associated with overall survival (responders: 364 days versus non‐responders: 24 days, P = 0.018). Venetoclax monotherapy is safe and is able to induce durable responses in elderly patients with secondary AML after treatment failure with HMA.     

Clinical studies of acute myeloid leukemia in the Japan Adult Leukemia Study Group

Acute myeloid leukemia (AML) is the most common adult leukemia in Japan. The treatment for AML consists of induction, consolidation, and maintenance therapies. To improve outcomes in the treatment of AML, the Japan Adult Leukemia Study Group has conducted six studies in AML patients aged 15-64?years since 1987. In AML201 study, IDR (12?mg/m(2)/day for 3?days) or DNR (50?mg/m(2)/day for 5?days) in combination with Ara-C (100?mg/m(2)/day continuous infusion for 7?days) was established as the standard induction therapy, and four courses of combination chemotherapy using non-cross-resistant agents for non-core binding factor (CBF) AML or three courses of high-dose Ara-C for CBF AML was established as the standard consolidation therapy. The AML97 study showed that allo-HSCT from an HLA-identical sibling donor reduced relapse incidence and improved disease-free survival (DFS), but did not significantly impact overall survival (OS) in poor or intermediate risk patients. Despite these studies by JALSG, only about one-third of AML patients remain free of disease for more than 7?years. The JALSG is now conducting the AML209 study to adapt individual therapies according to genetic alterations.     

Feasibility of BAALC gene expression for detection of minimal residual disease and risk stratification in normal karyotype acute myeloid leukaemia

High BAALC gene expression has been associated with poor prognosis in cytogenetically normal acute myeloid leukaemia (CN‐AML) and has been suggested as a suitable marker for assessing minimal residual disease (MRD). The purpose of this study was to substantiate these findings by the analysis of a large data set of 632 diagnostic and follow‐up samples in 142 intensively treated CN‐AML patients. Paired diagnostic/relapse samples of 35 patients revealed stable high BAALC expression in 89%, irrespective of a high proportion of clonal evolution found in 49% of these cases. High BAALC expression, both directly after induction chemotherapy and within 3–6 months after induction chemotherapy, correlated significantly with shorter event‐free survival and overall survival. Moreover, 8 of 10 patients displaying high BAALC expression levels after completion of induction therapy as well as 5 of 5 patients exhibiting high BAALC expression levels within 3–6 months after induction chemotherapy experienced relapse with a median of 197 and 101 days, respectively, from sampling to relapse. Thus, BAALC expression‐based MRD detection during therapy may be considered a strategy to identify patients at high risk of relapse.     

Quantitation of minimal residual disease in t(8;21)-positive acute myelogenous leukemia patients using real-time quantitative RT-PCR

t(8;21) is one of the common chromosomal translocations in acute myelogenous leukemia (AML). Using a recently developed real-time quantitative polymerase chain reaction (PCR) system, we analyzed the minimal residual disease (MRD) in bone marrow samples from seven AML patients with t(8;21) at different time points during the clinical courses of their disease. Four of these patients received chemotherapy and allogenic bone marrow transplantation (allo-BMT), and the other three were treated with chemotherapy alone. Two of the patients that received allo-BMT suffered a relapse. In these patients, the levels of AML1-MTG8 mRNA expression were shown to quantitatively increase. After re-induction chemotherapy and donor lymphocyte infusion therapy, AML went into remission and the expression levels decreased. In the other two patients receiving allo-BMT, the disease went into remission and the level of AML1-MTG8 mRNA expression remained under the detectable range. The other three patients received several courses of chemotherapy, without allo-BMT, and all of them clinically reached the hematological and cytogenetic remission state. However, there were low but detectable levels of MRD in their bone marrow samples. These results suggest that the real-time quantitative PCR assay is very useful for the monitoring of MRD and detecting an early relapse. This assay may also be useful in determining the quantitative difference in myelo-ablative activity between the chemotherapy alone and chemotherapy in conjunction with allo-BMT.     

Complex karyotype,older age,and reduced first‐line dose intensity determine poor survival in core binding factor acute myeloid leukemia patients with long‐term follow‐up

Approximately 40% of patients affected by core binding factor (CBF) acute myeloid leukemia (AML) ultimately die from the disease. Few prognostic markers have been identified. We reviewed 192 patients with CBF AML, treated with curative intent (age, 15–79 years) in 11 Italian institutions. Overall, 10‐year overall survival (OS), disease‐free survival (DFS), and event‐free survival were 63.9%, 54.8%, and 49.9%, respectively; patients with the t(8;21) and inv(16) chromosomal rearrangements exhibited significant differences at diagnosis. Despite similar high complete remission (CR) rate, patients with inv(16) experienced superior DFS and a high chance of achieving a second CR, often leading to prolonged OS also after relapse. We found that a complex karyotype (i.e., ≥4 cytogenetic anomalies) affected survival, even if only in univariate analysis; the KIT D816 mutation predicted worse prognosis, but only in patients with the t(8;21) rearrangement, whereas FLT3 mutations had no prognostic impact. We then observed increasingly better survival with more intense first‐line therapy, in some high‐risk patients including autologous or allogeneic hematopoietic stem cell transplantation. In multivariate analysis, age, severe thrombocytopenia, elevated lactate dehydrogenase levels, and failure to achieve CR after induction independently predicted longer OS, whereas complex karyotype predicted shorter OS only in univariate analysis. The achievement of minimal residual disease negativity predicted better OS and DFS. Long‐term survival was observed also in a minority of elderly patients who received intensive consolidation. All considered, we identified among CBF AML patients a subgroup with poorer prognosis who might benefit from more intense first‐line treatment. Am. J. Hematol. 90:515–523, 2015. © 2015 Wiley Periodicals, Inc.     

Determination of relapse risk based on assessment of minimal residual disease during complete remission by multiparameter flow cytometry in unselected patients with acute myeloid leukemia

Quantification of minimal residual disease (MRD) reveals significant prognostic information in patients treated for acute myeloid leukemia (AML). The application of multiparameter flow cytometry (MFC) for MRD assessment has resulted in significant prognostic information in selected cases in previous analyses. We analyzed MRD in unselected patients with AML in complete remission (CR) after induction (n = 58) and consolidation (n = 62) therapies. By using a comprehensive panel of monoclonal antibodies we identified at least one leukemia-associated aberrant immunophenotype (LAIP) in each patient. The degree of reduction between diagnosis and CR in LAIP-positive cells (log difference [LD]) as a continuous variable was significantly related to relapse-free survival (RFS) both after induction (P = .0001) and consolidation (P = .000 08) therapies, respectively. The LD determined after consolidation therapy was the only parameter related to overall survival (OS) (P = .005). Separation of patients based on the 75th percentile of LD after consolidation therapy resulted in groups with highly different RFS (83.3% versus 25.7%, P = .0034) and OS (87.5% versus 51.4%, P = .0507) at 2 years. Multivariate analysis identified LD as an independent prognostic factor for RFS at both checkpoints. MFC-based quantification of MRD reveals important prognostic information in unselected patients with AML in addition to cytogenetics and should be further evaluated and used in clinical trials.     

Prognostic impact of minimal residual disease analysis by flow cytometry in patients with acute myeloid leukemia before and after allogeneic hemopoietic stem cell transplantation

Allogeneic stem cell transplantation (allo‐SCT) has become the treatment of choice in patients with intermediate‐risk and high‐risk acute myeloid leukemia (AML). The quality of response to treatment, assessed in terms of detection of minimal residual disease (MRD), has been consistently associated with prognosis and clinical outcome in patients with AML. The aim of the present study was to evaluate the prognostic impact of analyzing MRD in bone marrow using 4‐color multiparametric flow cytometry (MFC) in 29 patients with AML before and after allo‐SCT. Eighteen patients who were shown to be MRD‐negative [≤0.1% leukemia‐associated immunophenotypes (LAIPs)] by MFC at transplantation and underwent allo‐SCT had lower rates of relapse (15% vs. 66%, P = 0.045), better overall 1‐yr survival (83% vs. 52%, P = 0.021) and a lower cumulative incidence of relapse (P = 0.032) than patients who were MRD‐positive (>0.1%). All post‐transplant MRD‐positive patients underwent a therapeutic intervention after transplant (tapering of immunosuppression, donor lymphocyte infusion, or re‐transplant) with the intention of preventing relapse. Disease was controlled and MRD disappeared in five of these patients. Disease recurred in the other seven patients. We can conclude that follow‐up with MFC for the detection of MRD in AML before and after SCT is useful for predicting relapse. In the post‐transplant setting, monitoring of MRD by MFC could be a key preemptive intervention.     

Impact of persistent minimal residual disease post‐consolidation therapy in children and adolescents with advanced Burkitt leukaemia: a Children's Oncology Group Pilot Study Report

Patient‐specific primers from 10 children/adolescents with Burkitt leukaemia (BL) ± central nervous system disease who were treated with French‐British‐American/Lymphome Malins de Burkitt 96 C1 plus rituximab were developed from diagnostic blood/bone marrow. Minimal residual disease (MRD) was assessed by real‐time polymerase chain reaction at the end of induction (EOI) and consolidation (EOC). Seventy per cent (7/10) and 71% (5/7) were MRD‐positive at EOI and EOC, respectively, with no disease recurrences. MRD after induction and consolidation did not predict relapse and subsequent therapy appeared to eliminate MRD. Thus, assessing MRD at a later time point is warranted in future trials to determine its clinical significance.     

Is the current consolidation regimen for AML evidence-based?

Current standard of care for consolidation therapy for AML varies based on age and induction regimen, among other factors. Many trials have sought to determine the optimal dose, number of cycles, and schedule for consolidation with cytarabine. For AML patients under age 60, mid-dose cytarabine is as effective as high-dose cytarabine, results after 3 or 4 cycles of cytarabine in consolidation are comparable but are both superior to only one cycle, and giving cytarabine every 12 h on days 1, 2, and 3 appears to have the same benefit but less toxicity than cytarabine given on days 1, 3, and 5. For those over age 60, the best dose of cytarabine is unknown, but post-remission therapy appears to improve survival for some patients who achieve remission after standard induction, depending on induction regimen used and MRD status at time of remission.     

Gemtuzumab ozogamicin with fludarabine,cytarabine, and granulocyte colony stimulating factor (FLAG‐GO) as front‐line regimen in patients with core binding factor acute myelogenous leukemia

Despite being considered “good‐risk” acute myelogenous leukemia (AML), long term outcomes in core binding factor (CBF) AML suggest room for improvement. We report on a regimen consisting of fludarabine, cytarabine, granulocyte colony stimulating factor, and low dose gemtuzumab ozogamicin (FLAG‐GO) as front‐line therapy of patients with CBF AML. Forty‐five patients were enrolled (median age 48 years). Remission rate was 95% with 5% induction deaths. The overall survival (OS) and relapse free survival (RFS) probability at 3 years are 78% and 85%, respectively. FLAG‐GO regimen results in high rates of RFS and OS in CBF AML. Our data along with recent data from several large groups strongly argues in favor of incorporation of gemtuzumab ozogamicin in frontline regimens for CBF AML. Am. J. Hematol. 89:964–968, 2014. © 2014 Wiley Periodicals, Inc.     

Predictive role of minimal residual disease and log clearance in acute myeloid leukemia: a comparison between multiparameter flow cytometry and Wilm’s tumor 1 levels

In acute myeloid leukemia (AML), the detection of minimal residual disease (MRD) as well as the degree of log clearance similarly identifies patients with poor prognosis. No comparison was provided between the two approaches in order to identify the best one to monitor follow-up patients. In this study, MRD and clearance were assessed by both multiparameter flow cytometry (MFC) and WT1 expression at different time points on 45 AML patients achieving complete remission. Our results by WT1 expression showed that log clearance lower than 1.96 after induction predicted the recurrence better than MRD higher than 77.0 copies WT1/10⁴ ABL. Conversely, on MFC, MRD higher than 0.2 % after consolidation was more predictive than log clearance below 2.64. At univariate and multivariate analysis, positive MRD values and log clearance below the optimal cutoffs were associated with a shorter disease-free survival (DFS). At the univariate analysis, positive MRD values were also associated with overall survival (OS). Therefore, post-induction log clearance by WT1 and post-consolidation MRD by MFC represented the most informative approaches to identify the relapse. At the optimal timing of assessment, positive MRD and log-clearance values lower than calculated thresholds similarly predicted an adverse prognosis in AML.     

Significance of recurrence of minimal residual disease detected by multi‐parameter flow cytometry in patients with acute lymphoblastic leukemia in morphological remission

We sought to determine the significance of minimal residual disease (MRD) relapse in patients with ALL after achieving MRD negative status following induction and consolidation therapy. Between January 2003 and September 2014, 647 newly diagnosed patients were treated [HyperCVAD‐based (n = 531); Augmented BFM (n = 116)]. Six hundred and one (93%) achieved complete remission (CR), and 546 (91%) became MRD negative. Fifty‐five patients [HyperCVAD‐based (n = 49); Augmented BFM (n = 6)] developed recurrence of MRD while still in morphological CR and are the subjects of this study. MRD was assessed by 6‐color (4‐color prior to 2009) multi‐parameter flow cytometry (MFC) at CR and multiple time points thereafter. Their median age was 44 years (range, 18–72 years), median WBC at initial presentation was 7.3 K/µL^?1 (range, 0.6–303.8 K/µL^?1) and median bone marrow blast percentage 88% (range, 26–98%). The median time to MRD relapse was 14 months (range 3–58 months). Forty‐four (80%) patients subsequently developed morphological relapse after median of 3 months (range, <1–33 months) from detection of MRD recurrence. Treatments received after MRD positivity and prior to morphological relapse: 16 continued maintenance chemotherapy; 15 received late intensification; 9 allogeneic stem cell transplant, 9 changed chemotherapy, 6 no further therapy. Only six remain alive and in CR1 and nine are alive after morphological relapse. MRD relapse detected by MFC at any time after achieving CR is associated with a high risk for morphological relapse. SCT can result in long‐term remission in some patients. Prospective studies of long‐term MRD assessments, together with less toxic treatment strategies to eradicate MRD, are warranted.     

Measurable residual disease in patients undergoing allogeneic transplant for acute myeloid leukemia

The most common indication for allogeneic hematopoietic cell transplant (alloHCT) is maintenance of remission after initial treatment for patients with acute myeloid leukemia (AML). Loss of remission, relapse, remains however the most frequent cause of alloHCT failure. There is strong evidence that detectable persistent disease burden (“measurable residual disease”, MRD) in patients with AML in remission prior to alloHCT is associated with increased risk of post-transplant relapse. MRD status as a summative assessment of response to pre-transplant therapy may allow superior patient-personalized risk stratification compared with models solely incorporating pre-treatment variables. An optimal methodology for AML MRD detection has not yet been established, but molecular methods such as DNA-sequencing may have additional prognostic utility compared to current approaches. There is growing evidence that intervention on AML MRD positivity may improve post-transplant outcomes. New initiatives will generate actionable data on the clinical utility of AML MRD testing for patients undergoing alloHCT.     

Incidence of bacterial and fungal infections in newly diagnosed acute myeloid leukaemia patients younger than 65 yr treated with induction regimens including fludarabine: retrospective analysis of 224 cases

Objectives: Infections are the major cause of morbidity and mortality in patients with acute myeloid leukaemia (AML). They primarily occur during the first course of induction chemotherapy and may increase the risk of leukaemia relapse, due to a significant delay in consolidation therapy. The intensification of induction chemotherapy and the use of non‐conventional drugs such as fludarabine are considered responsible for the increased risk of infections. Methods: In this study, we retrospectively analysed the infections occurred in 224 newly diagnosed AML patients ≤65 yr, consecutively treated between 1997 and 2002 with an induction regimen including fludarabine, arabinosyl cytosine and idarubicin, with or without etoposide (FLAI/FLAIE), in the context of three multicentric prospective trials (AML97, AML99, AML02). Results: During the induction phase, 146 (65%) patients experienced fever of undetermined origin (FUO), 30 (13%) and 47 (21%) patients had Gram‐negative and positive bacteremias, respectively, and 10 (4%) patients developed a probable/proven invasive fungal infection (IFI). The fatality rate for Gram‐negative, Gram‐positive bacteremias and probable/proven IFI was 10%, 8% and 60% respectively. During consolidation, 75 (35%) patients had FUO, 43 (20%) and 40 (19%) patients had Gram‐negative and positive bacteremias, respectively, and 5 (2%) patients developed a probable/proven IFI. The fatality rate for Gram‐negative, Gram‐positive bacteremias and probable/proven IFI was 14%, 5% and 80% respectively. Interestingly, the overall incidence of microbiologically documented infections during induction was 38% and the incidence of probable/proven IFIs during the induction/consolidation programme was 7%. No infections caused by viruses or opportunistic pathogens were observed neither during induction, nor during consolidation. Conclusions: These data, although retrospectively collected, suggest that fludarabine‐based chemotherapy is not associated with an increased incidence of infections, in particular IFIs, compared to conventional regimens commonly used for AML induction.     

hMICL and CD123 in combination with a CD45/CD34/CD117 backbone – a universal marker combination for the detection of minimal residual disease in acute myeloid leukaemia

Real‐time quantitative polymerase chain reaction (qPCR) has been extensively validated for the detection of minimal residual disease (MRD) in acute myeloid leukaemia (AML). Meanwhile, multicolour flow cytometry (MFC) has received less attention because the so‐called leukaemia‐associated immunophenotypes (LAIPs) are generally of lower sensitivity and specificity, and prone to change during therapy. To improve MRD assessment by MFC, we here evaluate the combination of human Myeloid Inhibitory C‐type Lectin (hMICL, also termed C‐type lectin domain family 12, member A, CLEC12A) and CD 123 (also termed interleukin‐3 receptor alpha, IL3RA) in combination with CD34 and CD117 (KIT), as an MRD assay in pre‐clinical and clinical testing in 69 AML patients. Spiking experiments revealed that the assay could detect MRD down to 10^?4 in normal bone marrow with sensitivities equalling those of validated qPCR assays. Moreover, it provided at least one MFC MRD marker in 62/69 patients (90%). High levels of hMICL/CD123 LAIPs at the post‐induction time‐point were a strong prognostic marker for relapse in patients in haematological complete remission (P < 0·001). Finally, in post induction samples, hMICL/CD123 LAIPs were strongly correlated (r = 0·676, P = 0·0008) to applied qPCR targets. We conclude the hMICL/CD123‐based MFC assay is a promising MRD tool in AML.