Early MRD response as a prognostic factor in adult patients with acute lymphoblastic leukemia

Recommendations for the treatment and management of adult B-Cell acute lymphoblastic leukemia in Asia-Pacific: Outcomes from a pilot initiative

The outcomes of adult B-cell acute lymphoblastic leukemia (ALL) remain poor. Recent advancements in the field of leukemia research show potential for improved patient care. However, the adoption of research findings into clinical practice is fraught with practice- and country-specific challenges. The continued addition of new findings warrants critical evaluation for the feasibility of incorporation into clinical practice. A uniform set of evidence-based guidelines can favorably assist physicians in making optimal clinical decisions. Such a resource may also serve as a reference point for strategic planning of initiatives aimed at addressing critical barriers in the optimal management of B-cell ALL. This initiative was undertaken to seek a collaborative perspective and understand the existing challenges. Concordance-based recommendations were outlined through a systematic discussion on various aspects of treatment and management of adult B-cell ALL. The outcomes and experiences gained from this exercise will serve as a foundation for future efforts encompassing the more granular aspects of the management of B-cell ALL across the Asia-Pacific region.

Minimal Residual Disease Status Predicts Outcome in Patients With Previously Untreated Follicular Lymphoma: A Prospective Analysis of the Phase III GALLIUM Study

PURPOSE

We report an analysis of minimal residual/detectable disease (MRD) as a predictor of outcome in previously untreated patients with follicular lymphoma (FL) from the randomized, multicenter GALLIUM (ClinicalTrials.gov identifier: NCT01332968) trial.

PATIENTS AND METHODS

Patients received induction with obinutuzumab (G) or rituximab (R) plus bendamustine, or cyclophosphamide, doxorubicin, vincristine, prednisone (CHOP) or cyclophosphamide, vincristine, prednisone (CVP) chemotherapy, followed by maintenance with the same antibody in responders. MRD status was assessed at predefined time points (mid-induction [MI], end of induction [EOI], and at 4-6 monthly intervals during maintenance and follow-up). Patients with evaluable biomarker data at diagnosis were included in the survival analysis.

RESULTS

MRD positivity was associated with inferior progression-free survival (PFS) at MI (hazard ratio [HR], 3.03 [95% CI, 2.07 to 4.45]; P < .0001) and EOI (HR, 2.25 [95% CI, 1.53 to 3.32]; P < .0001). MRD response was higher after G- versus R-chemotherapy at MI (94.2% v 88.9%; P = .013) and at EOI (93.1% v 86.7%; P = .0077). Late responders (MI-positive/EOI-negative) had a significantly poorer PFS than early responders (MI-negative/EOI-negative; HR, 3.11 [95% CI, 1.75 to 5.52]; P = .00011). The smallest proportion of MRD positivity was observed in patients receiving bendamustine at MI (4.8% v 16.0% in those receiving CHOP; P < .0001). G appeared to compensate for less effective chemotherapy regimens, with similar MRD response rates observed across the G-chemo groups. During the maintenance period, more patients treated with R than with G were MRD-positive (R-CHOP, 20.7% v G-CHOP, 7.0%; R-CVP, 21.7% v G-CVP, 9.4%). Throughout maintenance, MRD positivity was associated with clinical relapse.

CONCLUSION

MRD status can determine outcome after induction and during maintenance, and MRD negativity is a prerequisite for long-term disease control in FL. The higher MRD responses after G- versus R-based treatment confirm more effective tumor cell clearance.

[Clinical significance of monitoring NUP98::NSD1 fusion genes before and after allogeneic hematopoietic stem cell transplantation]

Objective: This study aimed to observe the dynamic changes of NUP98::NSD1 expression before and after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . Moreover, the clinical value of measurable residual disease (MRD) was analyzed. Methods: Sixteen AML patients who were diagnosed with the NUP98::NSD1 fusion gene and received allo-HSCT at Peking University People's Hospital were included. The NUP98::NSD1 fusion gene and leukemia-associated immunophenotype (LAIP) were monitored before and after transplantation to evaluate their MRD status. Results: The median follow-up time for all patients was 526 days (139-1136 days) , with four patients (25.0%) experiencing hematological recurrence at a median of 474 days (283-607 days) after transplantation. Three patients (18.8%) died, two of whom (12.5%) died of leukemia recurrence. The median expression level of NUP98::NSD1 in newly diagnosed patients with complete data was 78.5% (18.9%-184.4%) at the time of initial diagnosis. The recurrence rate was higher in NUP98::NSD1-positive patients after transplantation, with 44.4% of patients experiencing recurrence, whereas no recurrence occurred in NUP98::NSD1-negative patients after transplantation. The area under the receiver operating characteristic curve predicted by the NUP98::NSD1 level after transplantation was 1.000 (95% confidence interval: 1.000-1.000, P=0.003) . Among the four patients with recurrence, NUP98::NSD1 was more sensitive than flow cytometry residual (FCM) and Wilms' tumor gene 1 (WT1) . Conclusions: The NUP98::NSD1 fusion gene can be used to evaluate the MRD status of allo-HSCT. NUP98::NSD1-positive patients after transplantation have a high relapse rate and poor prognosis. NUP98::NSD1 was more sensitive than FCM and WT1 in predicting posttransplant relapse.

SET-CAN/NUP214 fusion gene in leukemia: general features and clinical advances

SET-CAN/NUP214 fusion is a recurrent event commonly observed in adult male patients diagnosed with T-cell acute lymphoblastic leukemia (T-ALL) and has occasionally been reported in other diseases such as acute myeloid leukemia (AML), myeloid sarcoma (MS), acute undifferentiated leukemia (AUL), chronic myeloid leukemia (CML) and B-cell acute lymphoblastic leukemia (B-ALL). This fusion gene is derived from chromosome del(9)(q34.11;q34.13) or t(9;9)(q34;q34) and may have an inhibitory effect on primitive progenitor differentiation. The prognosis of the reported patients is varied, with these patients often show resistance to chemotherapy regimens that include high doses of glucocorticoids. The optional treatment has not been determined, more cases need to be accumulated and evaluated. The scope of this review is to summarize the general features and prognostic significance in leukemia associated with the SET-CAN/NUP214 fusion gene and to discuss the methods of detection and treatment, aiming at providing some useful references for relevant researchers in the field of blood tumor.

Real-world utility of early measurable residual disease assessments by multi-parametric flow cytometry in adult patients with B-lymphoblastic leukemia receiving Hyper-CVAD induction chemotherapy

Multi-parametric flow cytometry (MFC) has a well-established role in measurable residual disease (MRD) monitoring in patients with B-lymphoblastic leukemia (B-ALL). However, the optimal time-point (TP) for early MRD testing and associated prognostic impact remain undefined in adult B-ALL patients receiving Hyper-CVAD induction chemotherapy. To evaluate the utility of MRD analysis after one cycle (TP1) in comparison to MRD analysis after two cycles (TP2) of induction treatment with Hyper-CVAD chemotherapy, we studied 49 adult B-ALL patients over a 10-year period (2010-2020) who had available bone marrow samples for morphological and MFC MRD assessments at the two separate TPs. Median times to TP1 and TP2 relative to start of treatment were 21 and 45 days, respectively. When censored at transplant, achievement of MRD negativity at TP1 was not associated with a statistically significant improvement in either event-free survival (EFS) (p = .426) or overall survival (OS) (p = .335) when compared to patients with MRD positivity. In contrast, achieving MRD negativity at TP2 was associated with a statistically significant improvement in both EFS (p = ·005) and OS (p = .047) over patients who remained MRD positive. Multivariate analysis demonstrated that KMT2A-rearrangement and MRD positivity at TP2 were the only significant predictors of outcome, correlating with worse EFS and OS. Therefore, in the absence of residual morphologic disease, MRD analysis after one cycle of Hyper-CVAD induction chemotherapy did not provide additional benefit with regard to risk stratification or correlation with survival outcomes when compared to MRD testing after two cycles of Hyper-CVAD in adult B-ALL patients.

Low levels of minimal residual disease after induction chemotherapy for BCR-ABL1-negative acute lymphoblastic leukaemia in adults are clinically relevant

The aim of the present study was to evaluate the significance of low-level minimal/measurable residual disease (MRD) during early consolidation treatment in adult BCR-ABL1-negative acute lymphoblastic leukaemia. The MRD load was monitored by immunoglobulin/T-cell receptor rearrangements and assessed as negative [complete MRD response (CMR)], positive non-quantifiable (MRDnq) and positive quantifiable (MRDq). MRDnq before the first and second consolidation blocks had a comparable negative effect on survival as MRDq. The 5-year overall survival for CMR, MRDnq and MRDq at week 11 was 74·0%, 42·3% and 35·0% respectively. No central nervous system infiltration and MRD at week 11 were independent prognostic factors for survival on multivariate analysis (hazard ratios 0·32 and 2·25).

Prognostic significance of SET-NUP214 fusion gene in acute leukemia after allogeneic hematopoietic stem cell transplantation

The SET nuclear proto-oncogene (SET)-nucleoporin (NUP) 214 fusion gene (SET-NUP214) is a rare leukemia fusion gene. Due to the limited number of samples with SET-NUP214 fusion gene in previous studies, the significance of SET-NUP214 for measurable residual disease (MRD) monitoring in patients with acute leukemia (AL) is still unclear. Our study aimed to observe the dynamic changes in SET-NUP214 expression before and after allogeneic hematopoietic stem cell transplantation (allo-HSCT), and analyzed whether SET-NUP214 could be used to evaluate MRD status. Our study included 24 AL patients who were newly diagnosed with SET-NUP214 fusion gene and they all received allo-HSCT. Their MRD was evaluated by monitoring SET-NUP214 fusion gene and leukemia-associated immunophenotype (LAIP). The median follow-up time was 501 days (56-2208 days). Of the enrolled patients, 6 (25%) patients died, including 3 (12.5%) patients died of leukemia relapse. Total 5 (20.8%) patients experienced hematological relapse at a median of 225 days (56-1057 days) post-transplantation. The SET-NUP214 median expression level at diagnosis was 405.1% (14.6%-1482.4%). SET-NUP214 gene expression generally became positive prior to flow cytometry results. In addition, the Kaplan-Meier survival curves analysis showed that those who had SET-NUP214 positive (SET-NUP214+) post-transplantation had a higher 2-year cumulative incidence of leukemia relapse (CIR) of 43.7 ± 18.8% (P < .05). However, there was no significant difference between SET-NUP214 positive and SET-NUP214 negative patients with regard to their 2-year overall survival (OS) (82.5 ± 11.3 vs 64.6 ± 17.5%, respectively, P = .271). ROC curve analysis turned out that the area under the ROC curve (AUC) was 0.916 (95% CI: 0.784-1.0; P = .005). In conclusion, SET-NUP214 fusion gene determined by real-time quantitative reverse transcriptase polymerase chain reaction (RQ-PCR) could be used to evaluate MRD status after allo-HSCT. Patients with positive SET-NUP214 expression after transplantation will have a poor prognosis.

Minimal Residual Disease in Acute Lymphoblastic Leukemia: Technical and Clinical Advances

Introduction: Acute lymphoblastic leukemia (ALL) is the first neoplasm where the assessment of early response to therapy by minimal residual disease (MRD) monitoring has proven to be a fundamental tool to guide therapeutic choices. The most standardized methods to study MRD in ALL are multi-parametric flow cytometry (MFC) and polymerase chain reaction (PCR) amplification-based methods. Emerging technologies hold the promise to improve MRD detection in ALL patients. Moreover, novel therapies, such as monoclonal antibodies, bispecific T-cell engagers, and chimeric antigen receptor T cells (CART) represent exciting advancements in the management of B-cell precursor (BCP)-ALL.

Aims: Through a review of the literature and in house data, we analyze the current status of MRD assessment in ALL to better understand how some of its limitations could be overcome by emerging molecular technologies. Furthermore, we highlight the future role of MRD monitoring in the context of personalized protocols, taking into account the genetic complexity in ALL.

Results and Conclusions: Molecular rearrangements (gene fusions and immunoglobulin and T-cell receptor-IG/TR gene rearrangements) are widely used as targets to detect residual leukemic cells in ALL patients. The advent of novel techniques, namely next generation flow cytometry (NGF), digital-droplet-PCR (ddPCR), and next generation sequencing (NGS) appear important tools to evaluate MRD in ALL, since they have the potential to overcome the limitations of standard approaches. It is likely that in the forthcoming future these techniques will be incorporated in clinical trials, at least at decisional time points. Finally, the advent of new powerful compounds is further increasing MRD negativity rates, with benefits in long-term survival and a potential reduction of therapy-related toxicities. However, the prognostic relevance in the setting of novel immunotherapies still needs to be evaluated.

[The prognostic significance of minimal residual disease detection after first induction treatment in adult acute lymphoblastic leukemia patients treated with autologous stem cell transplantation]

Objective: To investigate the prognostic significance of detection of minimal residual disease after first induction treatment (MRD(1)) in adult acute lymphoblastic leukemia (ALL) patients treated with autologous stem cell transplantation (auto-HSCT). Methods: The clinical data of 87 ALL patients who underwent auto-HSCT during February 2006 to April 2017 with MRD(1) detection data by flow cytometry were analyzed retrospectively. The relationship between MRD(1) and relapse and survival of ALL patients after auto-HSCT was studied. Results: Of 87 patients, 26 (29.9%) were MRD(1) positive. The proportion of high-risk immunophenotype (pro-B, pro-T, pre-T, mature T) was significantly higher in MRD(1)-positive patients than that in MRD(1) negative patients (34.6% vs 14.5%, P=0.038). There was no significant difference between positive and negative MRD(1) patients at age, sex, lineage (T/B), immunophenotype (standard risk/high risk), high white blood cell count (B-ALL>30×10(9)/L or T-ALL>100×10(9)/L), high-risk chromosome/gene ratio, the time from first complete remission to transplantation and pre-treatment regimen. The 5-year overall survival (OS) and leukemia-free survival (LFS) in MRD(1) negative and positive patients were 72.7% vs 47.3% (P=0.004) and 75.7% vs 29.6% (P<0.001), respectively. Multivariate analysis showed that positive MRD(1) was an independent risk factor for OS (HR=3.007, 95% CI 1.256-7.200, P=0.013) , and positive MRD(1) and high-risk immunophenotype were risk factors for LFS (HR=3.986, 95% CI 1.813-8.764, P=0.001; HR=2.981, 95% CI 1.373-6.473, P=0.006) . Conclusions: Auto-HSCT could not reverse the poor prognosis of MRD(1) positive patients. Auto-HSCT treatment is optional for patients with MRD(1) negative and maintaining MRD(1) negative status during intensive therapy.

Reduced Intensity Conditioning Allogeneic Hematopoietic Stem Cell Transplantation for Acute Lymphoblastic Leukemia; Current Evidence, and Improving Outcomes Going Forward

PURPOSE OF REVIEW

Outcomes for older adults with acute lymphoblastic leukemia (ALL) remain poor, and allogeneic hematopoietic stem cell transplant (HSCT) remains a potentially curative modality. However, benefits are offset by high rates of non-relapse mortality (NRM) in patients undergoing myeloablative conditioning (MAC) regimens. Reduced intensity conditioning (RIC) regimens can extend this therapy to adults who are unfit for MAC, although at the cost of higher relapse rates. In this review, we discuss evidence to support the usage of RIC regimens, controversies, and potential strategies to improve transplant outcomes going forward.

RECENT FINDINGS

Several novel therapies have recently been approved for the treatment of relapsed ALL and may play an important role in bridging adults with residual disease to RIC transplant. Assessing response to initial therapy via minimal residual disease (MRD) monitoring may determine which patients will derive the most benefit from allogeneic HSCT. Reduced intensity allogeneic HSCT remains a potentially curative therapy that can be offered to older adults however challenges remain. Going forward, MRD testing and novel therapies may help better select which patients should proceed to transplant and assist in getting those patients to transplant with optimally controlled disease.

Comparison of Real-time Quantitative Polymerase Chain Reaction and Eight-color Flow Cytometry in Assessment of Minimal Residual Disease in Adult Acute Lymphoblastic Leukemia

BACKGROUND

Minimal residual disease (MRD) is an important prognostic maker in acute lymphoblastic leukemia (ALL). However, few data comparing the measurement of adult ALL MRD using different methods in daily practice are available. We conducted an analysis comparing the importance of flow cytometry (FCM) and real-time quantitative polymerase chain reaction (PCR) in the assessment of MRD in adult ALL.

PATIENTS AND METHODS

Fifty-six consecutive adult patients with both Philadelphia-negative and -positive ALL treated according to an intensive protocol were enrolled in the study. Bone marrow samples were acquired on day 26 and during week 11 of treatment. MRD evaluation was performed using 8-color FCM and PCR of immunoglobulin or T-cell receptor gene clonal rearrangements and BCR-ABL1, KMT2A-AF4 and E2A-PBX1 fusion genes.

RESULTS

On day 26, both FCM and PCR seemed to have good discrimination sensitivity for overall survival (P = .001 to .008) and progression-free survival (P = .03 to .04) prediction for both Philadelphia-positive and -negative cases. The most sensitive method in week 11 was PCR including all results > 0 considered to indicate MRD positivity (P = .002 for overall survival and P = .02 for progression-free survival). PCR with other cutoffs was not sufficiently sensitive in week 11. Moreover, no FCM⁺ samples were found in week 11. The subanalysis of the Philadelphia-negative patients showed similar results.

CONCLUSION

Our analysis showed that both FCM and PCR MRD assessment methods are sensitive for survival prediction during induction. However, we believe FCM could not be sufficiently sensitive in later phases of treatment.

The prognostic role of E2A-PBX1 expression detected by real-time quantitative reverse transcriptase polymerase chain reaction (RQ-PCR) in B cell acute lymphoblastic leukemia after allogeneic hematopoietic stem cell transplantation

The E2A-PBX1 rearrangement is common in B cell acute lymphoblastic leukemia (B-ALL). However, whether this fusion gene can be used as a reliable marker for minimal residual disease (MRD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains unknown. In this study, clinical data were collected from 28 consecutive B-ALL patients who received allo-HSCT. Their MRD was evaluated by E2A-PBX1 and leukemia-associated immunophenotype (LAIP). The median follow-up was 374 days (55-2342 days). Of the enrolled patients, seven (25%) patients died of leukemia relapse. A total of nine (32.1%) patients experienced relapse at a median of 164 days (75-559 days) after transplantation. The median expression level in the first positive sample was 0.14% (0.0071-902.4%). The duration from E2A-PBX1-positive results to hematological relapse was 74 days (30-469 days). E2A-PBX1 expression generally became positive prior to flow cytometry. Patients with positive E2A-PBX1 gene expression pre-transplantation were more likely to have positive E2A-PBX1 expression after transplantation. Taken all together, E2A-PBX1 expression determined by real-time quantitative reverse transcriptase polymerase chain reaction (RQ-PCR) could be used to evaluate MRD status after allo-HSCT. Patients with positive E2A-PBX1 expression after transplant will have a poor prognosis.

Minimal residual disease in adult ALL: technical aspects and implications for correct clinical interpretation

Nowadays, minimal residual disease (MRD) is accepted as the strongest independent prognostic factor in acute lymphoblastic leukemia (ALL). It can be detected by molecular methods that use leukemia-specific or patient-specific molecular markers (fusion gene transcripts, or immunoglobulin/T-cell receptor [IG/TR] gene rearrangements), and by multi-parametric flow cytometry. The sensitivity and specificity of these methods can vary across treatment time points and therapeutic settings. Thus, knowledge of the principles and limitations of each technology is of the utmost importance for correct interpretation of MRD results. Time will tell whether new molecular and flow cytometric high-throughput technologies can overcome the limitations of current standard methods and eventually bring additional benefits. MRD during standard ALL chemotherapy is the strongest overall prognostic indicator and has therefore been used for refining initial treatment stratification. Moreover, MRD positivity after the maintenance phase of treatment may point to an impending relapse and thus enable salvage treatment to be initiated earlier, which could possibly improve treatment results. The prognostic relevance of pretransplantation MRD was shown by several studies, and MRD high-risk patients were shown to benefit from stem cell transplantation (SCT). Also, MRD positivity after SCT correlates with worse outcomes. In addition, MRD information is very instructive in current clinical trials that test novel agents to evaluate their treatment efficacy. Although conventional clinical risk factors lose their independent prognostic significance when combined with MRD information, recently identified genetic markers may further improve the treatment stratification in ALL.

Minimal residual disease in adult ALL: technical aspects and implications for correct clinical interpretation

Nowadays, minimal residual disease (MRD) is accepted as the strongest independent prognostic factor in acute lymphoblastic leukemia (ALL). It can be detected by molecular methods that use leukemia-specific or patient-specific molecular markers (fusion gene transcripts, or immunoglobulin/T-cell receptor [IG/TR] gene rearrangements), and by multi-parametric flow cytometry. The sensitivity and specificity of these methods can vary across treatment time points and therapeutic settings. Thus, knowledge of the principles and limitations of each technology is of the utmost importance for correct interpretation of MRD results. Time will tell whether new molecular and flow cytometric high-throughput technologies can overcome the limitations of current standard methods and eventually bring additional benefits. MRD during standard ALL chemotherapy is the strongest overall prognostic indicator and has therefore been used for refining initial treatment stratification. Moreover, MRD positivity after the maintenance phase of treatment may point to an impending relapse and thus enable salvage treatment to be initiated earlier, which could possibly improve treatment results. The prognostic relevance of pretransplantation MRD was shown by several studies, and MRD high-risk patients were shown to benefit from stem cell transplantation (SCT). Also, MRD positivity after SCT correlates with worse outcomes. In addition, MRD information is very instructive in current clinical trials that test novel agents to evaluate their treatment efficacy. Although conventional clinical risk factors lose their independent prognostic significance when combined with MRD information, recently identified genetic markers may further improve the treatment stratification in ALL.

An update on PCR use for minimal residual disease monitoring in acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is the first neoplasm where the assessment of early response to therapy by minimal residual disease (MRD) monitoring has proven to be a fundamental tool for guiding therapeutic choices. In recent years, thanks to real-time quantitative PCR (qPCR), MRD monitoring has further achieved higher levels of sensitivity and standardization. However, some outstanding issues still remain to be addressed and emerging technologies hold the promise of improving MRD detection in ALL patients. Areas covered: Through a comprehensive review of the literature, we analyze the state-of-the-art of molecular MRD assessment in ALL to better understand how, in the upcoming years, some of its limitations could be tackled by emerging molecular technologies. Furthermore, we highlight the future role of molecular MRD monitoring in the context of personalized protocols, taking into account the growing genetic complexity in ALL. Expert commentary: Although new molecular technologies are promising tools for MRD assessment, qPCR still remains the gold standard for evaluating MRD in ALL. High-throughput sequencing and droplet digital PCR allow to identify new prognostic factors and/or MRD targets at diagnosis and to perform earlier MRD evaluations, thereby optimizing patient stratification and earlier MRD-based clinical intervention to improve ALL patient outcomes.

Prognostic significance of IKZF1 deletion in adult B cell acute lymphoblastic leukemia: a meta-analysis

The IKAROS family zinc finger 1 (IKZF1) gene is frequently altered in adults with B cell acute lymphoblastic leukemia (ALL). Although many studies have indicated that IKZF1 alterations might be associated with poor outcomes in adults with ALL, the results remain controversial. A previous meta-analysis demonstrated the negative prognostic significance of IKZF1 deletion in ALL. However, most of the included studies (14 out of 15) were conducted in pediatric patients with ALL, and age was identified as a significant source of heterogeneity. Thus, performing the present meta-analysis provides valuable information to further elucidate the prognostic value of IKZF1 deletion in adults with ALL. Eight studies were identified that had been published prior to August 1, 2016. The studies included a total of 1008 patients. Hazard ratios (HRs) with 95% confidence intervals (CIs) of overall survival (OS) and disease-free survival (DFS)/relapse-free survival (RFS)/progression-free survival (PFS)/event-free survival (EFS) were pooled to estimate the prognostic power of IKZF1 deletion. Pooled HRs suggested that IKZF1 deletion had a negative impact on both OS (HR = 1.40, 95% CI 1.13-1.73) and DFS/RFS/PFS/EFS (HR = 1.67, 95% CI 1.28-2.17) in the overall population. Subgroup analyses indicated that IKZF1 deletion could independently predict unfavorable OS (HR = 1.60, 95% CI 1.25-2.06) and DFS/RFS/PFS/EFS (HR = 1.67, 95% CI 1.28-2.17) in BCR-ABL1-negative but not in BCR-ABL1-positive B cell ALL patients. Our meta-analysis suggests that IKZF1 deletion is a poor prognostic factor for adults with B cell ALL and may be more valuable in BCR-ABL1-negative B cell ALL patients.