Early prediction of response in patients with relapsed or refractory Philadelphia chromosome–positive acute lymphoblastic leukemia (Ph+ALL) treated with imatinib

Prediction of Response to FDA-Approved Targeted Therapy and Immunotherapy in Acute Lymphoblastic Leukemia (ALL)

OPINION STATEMENT

Acute lymphoblastic leukemia (ALL) represents the predominant cancer in pediatric populations, though its occurrence in adults is relatively rare. Pre-treatment risk stratification is crucial for predicting prognosis. Important factors for assessment include patient age, white blood cell (WBC) count at diagnosis, extramedullary involvement, immunophenotype, and cytogenetic aberrations. Minimal residual disease (MRD), primarily assessed by flow cytometry following remission, plays a substantial role in guiding management plans. Over the past decade, significant advancements in ALL outcomes have been witnessed. Conventional chemotherapy has remarkably reduced mortality rates; however, its intensive nature raises safety concerns and has led to the emergence of treatment-resistant cases with recurrence of relapses. Consequently, The U.S. Food and Drug Administration (FDA) has approved several novel treatments for relapsed/refractory ALL due to their demonstrated efficacy, as indicated by improved complete remission and survival rates. These treatments include tyrosine kinase inhibitors (TKIs), the anti-CD19 monoclonal antibody blinatumomab, anti-CD22 inotuzumab ozogamicin, anti-CD20 rituximab, and chimeric antigen receptor (CAR) T-cell therapy. Identifying the variables that influence treatment decisions is a pressing necessity for tailoring therapy based on heterogeneous patient characteristics. Key predictive factors identified in various observational studies and clinical trials include prelymphodepletion disease burden, complex genetic abnormalities, and MRD. Furthermore, the development of serious adverse events following treatment could be anticipated through predictive models, allowing for appropriate prophylactic measures to be considered. The ultimate aim is to incorporate the concept of precision medicine in the field of ALL through valid prediction platform to facilitate the selection of the most suitable treatment approach.

Double Philadelphia Chromosomes- A Rare, Yet an Important Cytogenetic Phenomenon of Prognostic Significance in De Novo Acute Lymphoblastic Leukemia

Presence of additional copies of Philadelphia chromosome (Ph) is characteristic of chronic myeloid leukemia in blast crisis, very rarely observed in de novo acute lymphoblastic leukemia (ALL). Ph positive (Ph+ve) ALL and CML in lymphoid blast crisis (CML-LBC) are biologically different with divergent clinical course. Double Ph+ve ALL has little data available as to its incidence and prognostic significance. We studied five cases of Ph+ve precursor B-cell ALL having an extra copy of Ph chromosome with regard to their clinical and laboratory features. An extensive review of literature was done on prognostic significance and molecular aspects of double Ph in ALL. The study confirms that double Ph was a rare phenomenon in precursor B-cell ALL. It is observed that molecular basis of double Ph positive ALL is less understood compared to CML in blast crisis. The study highlights fundamental role of cytogenetic and molecular studies in diagnosis and management of these patients. Long-term follow-up studies on a larger group of patients are required to understand the prognostic impact of extra Ph in Ph+ve ALL, which is usually resistant to standard chemotherapeutic regimen and often requiring bone marrow transplantation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-022-01525-1.

The first Japanese biobank of patient-derived pediatric acute lymphoblastic leukemia xenograft models

A lack of practical resources in Japan has limited preclinical discovery and testing of therapies for pediatric relapsed and refractory acute lymphoblastic leukemia (ALL), which has poor outcomes. Here, we established 57 patient-derived xenografts (PDXs) in NOD.Cg-Prkdc^scid ll2rg^tm1Sug /ShiJic (NOG) mice and created a biobank by preserving PDX cells including 3 extramedullary relapsed ALL PDXs. We demonstrated that our PDX mice and PDX cells mimicked the biological features of relapsed ALL and that PDX models reproduced treatment-mediated clonal selection. Our PDX biobank is a useful scientific resource for capturing drug sensitivity features of pediatric patients with ALL, providing an essential tool for the development of targeted therapies.

Nutlin-3 plus tanshinone IIA exhibits synergetic anti-leukemia effect with imatinib by reactivating p53 and inhibiting the AKT/mTOR pathway in Ph+ ALL

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) is triggered by BCR/ABL kinase. Recent efforts focused on the development of more potent tyrosine kinase inhibitors (TKIs) that also inhibit mutant tyrosine kinases such as nilotinib and dasatinib. Although major advances in the treatment of this aggressive disease with potent inhibitors of the BCR/ABL kinases, patients in remission frequently relapse due to drug resistance possibly mediated, at least in part, by compensatory activation of growth-signaling pathways and protective feedback signaling of leukemia cells in response to TKI treatment. Continuous activation of AKT/mTOR signaling and inactivation of p53 pathway were two mechanisms of TKI resistance. Here, we reported that nutlin-3 plus tanshinone IIA significantly potentiated the cytotoxic and apoptotic induction effects of imatinib by down-regulation of the AKT/mTOR pathway and reactivating the p53 pathway deeply in Ph+ ALL cell line. In primary samples from Ph+ ALL patients, nutlin-3 plus tanshinone IIA also exhibited synergetic cytotoxic effects with imatinib. Of note, three samples from Ph+ ALL patients harboring T315I mutation also showed sensitivity to the combined treatment of imatinib, nutlin-3 plus tanshinone IIA. In Ph+ ALL mouse models, imatinib combined with nutlin-3 plus tanshinone IIA also exhibited synergetic effects on reduction in leukemia burden. These results demonstrated that nutlin-3 plus tanshinone IIA combined TKI might be a promising treatment strategy for Ph+ ALL patients.

Diagnostic and treatment of adult Philadelphia chromosome-positive acute lymphoblastic leukemia

The outcome of adult patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) has improved substantially with the introduction of tyrosine kinase inhibitors (TKIs). TKIs are now integral components of therapy for Ph+ ALL. The current consensus is that they improve patient outcomes compared with historical control patients treated with chemotherapy alone, and increase the number of patients able to receive stem cell transplant. New challenges have emerged with respect to induction of resistance mainly via Abelson tyrosine kinase mutations. Several novel kinase inhibitors with significantly more potent antileukemic activity are currently being developed. Furthermore novel immune therapies, which recruit or modify patient's own T cells to fight leukemic cells, are being developed and could find an important place in Ph+ ALL therapy by few years. In this article, we reviewed treatment approaches in adults with Ph+ ALL with a focus on TKIs and combined chemotherapy regimens.

Evidence-based guidelines for the use of tyrosine kinase inhibitors in adults with Philadelphia chromosome-positive or BCR-ABL-positive acute lymphoblastic leukemia: a Canadian consensus

Adult Philadelphia chromosome-positive (Ph+) or BCR-ABL-positive (BCR-ABL+) acute lymphoblastic leukemia (all) is an acute leukemia previously associated with a high relapse rate, short disease-free survival, and poor overall survival. In adults, allogeneic hematopoietic cell transplant in first remission remains the only proven curative strategy for transplant-eligible patients. The introduction of tyrosine kinase inhibitors (tkis) in the treatment of patients with Ph+ or BCR-ABL+ all has significantly improved the depth and duration of complete remission, allowing more patients to proceed to transplantation. Although tkis are now considered a standard of care in this setting, few randomized trials have examined the optimal use of tkis in patients with Ph+ all. Questions of major importance remain, including the best way to administer these medications, the choice of tki to administer, and the schedule and the duration to use. We present the results of a systematic review of the literature with consensus recommendations based on the available evidence.

Current concepts in pediatric Philadelphia chromosome-positive acute lymphoblastic leukemia

The t(9;22)(q34;q11) or Philadelphia chromosome creates a BCR-ABL1 fusion gene encoding for a chimeric BCR-ABL1 protein. It is present in 3-4% of pediatric acute lymphoblastic leukemia (Ph(+) ALL), and about 25% of adult ALL cases. Prior to the advent of tyrosine kinase inhibitors (TKI), Ph(+) ALL was associated with a very poor prognosis despite the use of intensive chemotherapy and frequently hematopoietic stem-cell transplantation (HSCT) in first remission. The development of TKIs revolutionized the therapy of Ph(+) ALL. Addition of the first generation ABL1 class TKI imatinib to intensive chemotherapy dramatically increased the survival for children with Ph(+) ALL and established that many patients can be cured without HSCT. In parallel, the mechanistic understanding of Ph(+) ALL expanded exponentially through careful mapping of pathways downstream of BCR-ABL1, the discovery of mutations in master regulators of B-cell development such as IKZF1 (Ikaros), PAX5, and early B-cell factor (EBF), the recognition of the complex clonal architecture of Ph(+) ALL, and the delineation of genomic, epigenetic, and signaling abnormalities contributing to relapse and resistance. Still, many important basic and clinical questions remain unanswered. Current clinical trials are testing second generation TKIs in patients with newly diagnosed Ph(+) ALL. Neither the optimal duration of therapy nor the optimal chemotherapy backbone are currently defined. The role of HSCT in first remission and post-transplant TKI therapy also require further study. In addition, it will be crucial to continue to dig deeper into understanding Ph(+) ALL at a mechanistic level, and translate findings into complementary targeted approaches. Expanding targeted therapies hold great promise to decrease toxicity and improve survival in this high-risk disease, which provides a paradigm for how targeted therapies can be incorporated into treatment of other high-risk leukemias.

Current and future management of Ph/BCR-ABL positive ALL

Following the introduction of targeted therapy with tyrosine kinase inhibitors (TKI) at the beginning of the past decade, the outcome of patients with Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) has dramatically improved. Presently, the use of refined programs with first/second generation TKI's and chemotherapy together with allogeneic stem cell transplantation allow up to 50% of all patients to be cured. Further progress is expected with the new TKI ponatinib, overcoming resistance caused by T315I point mutation, other targeted therapies, autologous transplantation in molecularly negative patients, therapeutic monoclonal antibodies like inotuzumab ozogamicin and blinatumomab, and chimeric antigen receptor-modified T cells. Ph+ ALL could become curable in the near future even without allogeneic stem cell transplantation, minimizing the risk of therapy-related death and improving greatly the quality of patients' life.

Advanced targeted, cell and gene-therapy approaches for pediatric hematological malignancies: results and future perspectives

Despite the survival of pediatric patients affected by hematological malignancies being improved in the last 20 years by chemotherapy and hematopoietic stem cell transplantation, a significant amount of patients still relapses. Treatment intensification is limited by toxic side effects and is constrained by the plateau of efficacy, while the pipeline of new chemotherapeutic drugs is running short. Therefore, novel therapeutic strategies are essential and researchers around the world are testing in clinical trials immune and gene-therapy approaches as second-line treatments. The aim of this review is to give a glance at these novel promising strategies of advanced medicine in the field of pediatric leukemias. Results from clinical protocols using new targeted “smart” drugs, immunotherapy, and gene therapy are summarized, and important considerations regarding the combination of these novel approaches with standard treatments to promote safe and long-term cure are discussed.

Prevalence and dynamics of bcr-abl kinase domain mutations during imatinib treatment differ in patients with newly diagnosed and recurrent bcr-abl positive acute lymphoblastic leukemia

Imatinib is highly effective in newly diagnosed, but not in relapsed, Philadelphia chromosome positive acute lymphoblastic leukemia (Ph+ ALL). BCR-ABL tyrosine kinase domain (TKD) mutations are associated with acquired imatinib resistance, but their role in primary resistance is uncertain. Using highly sensitive ligation-PCR and denaturing high-performance liquid chromatography (DHPLC), we identified baseline TKD mutations in 21% and 42% of imatinib-naïve patients with newly diagnosed (n=26) or recurrent (n=65) Ph+ ALL, respectively (P=ns). Within 4 weeks of starting the imatinib treatment, absolute levels of mutant bcr-abl transcripts increased significantly in patients with advanced, but not with de novo, Ph+ ALL. The net expansion of pre-existing mutant clones during imatinib treatment resulted in the rapid appearance of initially undetectable TKD mutations, which after 4 weeks were detectable in 70% of patients with advanced disease. There was a high degree of concordance between the type of mutations detected at relapse and during initial imatinib treatment. The profoundly different outgrowth dynamics of leukemic clones with bcr-abl mutations in imatinib-treated patients who differ in their disease history, provides clinical-translational evidence for a contributory role of non-mutational resistance mechanisms, possibly induced by prior chemotherapy. Moreover, the prevalence of pre-existing, clinically relevant TKD may have been underestimated in tyrosine kinase inhibitor-naïve patients with Ph+ ALL.

Managing Philadelphia chromosome-positive acute lymphoblastic leukemia: role of tyrosine kinase inhibitors

Before the introduction of tyrosine kinase inhibitors, the prognosis for patients with Philadelphia chromosome-positive acute lymphoblastic leukemia was poor. The treatment of choice, stem cell transplantation, is a potentially curative option, but it is available only for a minority of patients and is associated with significant risk of morbidity and mortality. Although imatinib is largely effective, a substantial proportion of patients become resistant or intolerant to it. The activity of imatinib may be enhanced by coadministration with chemotherapy; such treatment is effective in many patients. Dasatinib is established as a second-line treatment in patients with resistance to or intolerance of imatinib. Recent data suggest that dasatinib, either alone or in combination with chemotherapy, has utility as first-line therapy. Dasatinib is more potent than imatinib, is less susceptible to drug-resistance mechanisms, and has been shown to penetrate the blood-brain barrier, making it potentially effective for treating central nervous system disease. Patients who relapse during treatment with dasatinib frequently carry the T315I mutation of BCR-ABL. Future regimens combining dasatinib with an agent able to inhibit this mutation may further improve outcome.

A pathway-based gene signature correlates with therapeutic response in adult patients with Philadelphia chromosome-positive acute lymphoblastic leukemia

Biomarkers to predict response to therapy in adults with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) are not yet established. In this study, we performed a meta-analysis of earlier genome-wide gene expression studies to identify pathway-based genes that are associated with therapeutic response. The predictive power of these genes was validated by transcript profiling in diagnostic bone marrow samples from Ph+ ALL patients using a quantitative real-time PCR array. Gene expression was correlated with cytogenetic and molecular characteristics, including presence of ABL1 mutations and IKZF1 deletion. A total of 43 de novo Ph+ ALL patients treated uniformly with tyrosine kinase inhibitors combined with chemotherapy were selected to validate 46 identified genes. A 9-gene signature was established to distinguish optimal responders from patients with persistent residual disease and early molecular recurrence. The signature was subsequently validated with 87% predictive accuracy in an independent validation set of patients. When initially optimal responders relapsed, their gene expression patterns also shifted. Optimal responders showed upregulation of genes involved in proliferation and apoptosis pathways, whereas poor responders had higher expression of genes that facilitate tumor cell survival in hypoxic conditions as well as development of drug resistance. This unique 9-gene signature may better enable stratification of patients to proper therapeutic regimens and provides new insights into mechanisms of Ph+ ALL response to therapy.

Philadelphia chromosome-positive acute lymphoblastic leukemia

The Philadelphia (Ph) chromosome, a short chromosome 22, is the most frequent cytogenetic abnormality in adult patients with acute lymphoblastic leukemia (ALL). It occurs in approximately 20% to 30% of adults and in about 5% of children with this disease. The incidence rises with age and occurs in approximately 50% of patients older than 50 years. This article reviews the treatment regimens for Ph+ ALL, including imatinib and second generation tyrosine kinase inhibitors (TKIs). The introduction of effective TKIs in the treatment of Ph+ ALL has introduced several avenues of research in a disease that was hitherto difficult to treat.

Concurrent intensive chemotherapy and imatinib before and after stem cell transplantation in newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia. Final results of the CSTIBES02 trial

BACKGROUND

Imatinib, given concurrently or alternating with chemotherapy, has improved the response and survival of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) but relapses are still frequent. The aim of this study was to evaluate the feasibility and results of giving imatinib concurrently with intensive chemotherapy, stem cell transplantation and post-transplant imatinib maintenance therapy in patients with newly diagnosed Ph(+) ALL.

DESIGN AND METHODS

This was a phase II study of patients with newly diagnosed Ph(+) ALL given standard chemotherapy, together with imatinib (400 mg/day) until stem cell transplantation, followed by imatinib maintenance therapy for all patients regardless of the molecular status of the disease.

RESULTS

Of the 30 patients included, 27 (90%) achieved complete remission, one was resistant to treatment and two died during induction therapy. The percentages of major and complete molecular responses were 86% and 21% after induction, and 81% and 65% after consolidation, respectively. Similar results were observed assessing minimal residual disease by flow cytometry. Of the 27 patients who achieved complete remission, 21 underwent stem cell transplantation (16 allogeneic, 5 autologous). Imatinib (400 mg/day) could be administered after transplantation for a median of 3.9 months in 12 patients, although it was interrupted in 10 patients (in 2 cases because of side effects of the drug). Nine patients relapsed, four before and five after stem cell transplantation and eight patients died of transplant-related causes. With a median follow-up of 4.1 years, the probabilities (95% CI) of disease-free and overall survival were 30% (15% to 45%) and 30% (16% to 45%), respectively.

CONCLUSIONS

These results confirm that imatinib is an effective first-line treatment for adult Ph(+) ALL when given concurrently with chemotherapy, making stem cell transplantation feasible in a high proportion of patients. However, post-transplantation imatinib administration was limited, mainly because of transplantation-derived complications rather than drug-specific toxicity.

Allogeneic hematopoietic cell transplantation for adult Philadelphia-positive acute lymphoblastic leukemia in the era of tyrosine kinase inhibitors

Allogeneic hematopoietic cell transplantation in first complete remission (CR1) is considered the standard of care, and the only established therapy that offers a possibility of cure for patients with Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL). Unfortunately, a number of patients, with suitable HLA-matched donors, are unable to receive an allograft because they fail to respond, or relapse shortly after induction chemotherapy. Incorporating imatinib during the induction/consolidation phase is facilitating a higher number of potentially curative allografts by improving both remission rates and/or the durability of responses in patients with Ph+ ALL. Imatinib and other tyrosine kinase inhibitors are also improving outcomes in elderly patients with Ph+ ALL, ineligible for allografting, when combined with glucocorticoids, and/or conventional chemotherapy. The addition of imatinib or other tyrosine kinase inhibitors to the therapeutic armamentarium of Ph+ ALL is reshaping the treatment algorithm and improving prognosis of this dreadful disease.

Tyrosine kinase inhibitors for the treatment of Philadelphia chromosome-positive adult acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a heterogeneous disorder, with the greatest prevalence in children, but it also affects adults, and has an increasing incidence with age. Chromosomal abnormalities in ALL have been frequently described, the most common is the Philadelphia chromosome (Ph). The resulting fusion gene, BCR-ABL1, encodes for a chimerical oncoprotein (BCR-ABL) with constitutive tyrosine kinase activity, which leads to uncontrolled cell proliferation, reduced apoptosis, and impaired cell adhesion. Treating Philadelphia chromosome-positive (Ph+) ALL patients with conventional chemotherapy has not substantially improved their long-term outcomes. Recently, however, BCR-ABL-targeted strategies have been successfully adopted. Imatinib is an oral competitive inhibitor of ABL with demonstrated phase 2 efficacy in patients with treatment-naive and pretreated ALL. Despite its efficacy, imatinib may induce specific resistance in a large proportion of patients, mainly because of the occurrence of ABL1 mutations. Therefore, novel inhibitors have been developed. Dasatinib is a multitargeted kinase inhibitor of BCR-ABL, SRC, C-KIT, PDGFRs, and ephrin A receptor kinases. Unlike imatinib, it binds both the active and inactive BCR-ABL as well as the majority of ABL mutants. Dasatinib is approved for treatment of imatinib-pretreated Ph+ ALL, and chronic myeloid leukemia (CML) on the basis of phase 2 trials that demonstrated impressive efficacy and favorable tolerability profiles. Nilotinib is another BCR-ABL targeted agent that is similar in structure to imatinib but has significantly greater binding affinity. It also has demonstrated promising efficacy in Ph+ ALL but is still being evaluated in phase 2 trials. In this article, the authors reviewed current knowledge on novel tyrosine-kinase inhibitors in adult Ph+ ALL patients.

Imatinib compared with chemotherapy as front-line treatment of elderly patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL)

BACKGROUND

Elderly patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) have a poor prognosis, with a low complete remission (CR) rate, high induction mortality, and short remission duration. Imatinib (IM) has a favorable toxicity profile but limited antileukemic activity in advanced Ph+ALL. Imatinib in combination with intensive chemotherapy has yielded promising results as front-line therapy, but its value as monotherapy in newly diagnosed Ph+ALL is not known.

METHODS

Patients with de novo Ph+ALL were randomly assigned to induction therapy with either imatinib (Ind(IM)) or multiagent, age-adapted chemotherapy (Ind(chemo)). Imatinib was subsequently coadministered with consolidation chemotherapy.

RESULTS

In all, 55 patients (median age, 68 years) were enrolled. The overall CR rate was 96.3% in patients randomly assigned to Ind(IM) and 50% in patients allocated to Ind(chemo) (P = .0001). Nine patients (34.6%) were refractory and 2 patients died during Ind(chemo); none failed imatinib induction. Severe adverse events were significantly more frequent during Ind(chemo) (90% vs 39%; P = .005). The estimated overall survival (OS) of all patients was 42% +/- 8% at 24 months, with no significant difference between the 2 cohorts. Median disease-free survival was significantly longer in the 43% of patients (21 of 49 evaluable) in whom BCR-ABL transcripts became undetectable (18.3 months vs 7.2 months; P = .002).

CONCLUSIONS

In elderly patients with de novo Ph+ALL, imatinib induction results in a significantly higher CR rate and lower toxicity than induction chemotherapy. With subsequent combined imatinib and chemotherapy consolidation, this initial benefit does not translate into improved survival compared with chemotherapy induction.

Dasatinib induces rapid hematologic and cytogenetic responses in adult patients with Philadelphia chromosome positive acute lymphoblastic leukemia with resistance or intolerance to imatinib: interim results of a phase 2 study

Patients with Philadelphia (Ph) chromosome-positive acute lymphoblastic leukemia (ALL) have a rapid disease course and a poor prognosis. Dasatinib, a novel, oral, multitargeted kinase inhibitor of BCR-ABL and SRC family kinases, has previously induced responses in patients with imatinib-resistant or -intolerant Ph-positive ALL. We present the interim results of a phase 2 study designed to further assess the efficacy, safety, and tolerability of dasatinib 140 mg in this patient population (n = 36). With a minimum follow-up of 8 months, treatment with dasatinib resulted in substantial hematologic and cytogenetic response rates. Major hematologic responses were achieved in 42% (15/36) of patients, 67% of whom remained progression-free. Complete cytogenetic responses were attained by 58% (21/36) of patients. The presence of BCR-ABL mutations conferring imatinib resistance did not preclude a response to dasatinib. Dasatinib was also tolerable, with 6% (2/36) of patients discontinuing therapy as a result of study-drug toxicity. Most adverse events (AEs) were grade 1 or 2; febrile neutropenia was the most frequent severe AE, but this and other cytopenias were manageable with dose reduction. Dasatinib represents a safe and effective treatment option and an important therapeutic advance for patients with Ph-positive ALL. This trial was registered at www.clinicaltrials.gov as #CA180015.

Kinase domain mutations of BCR-ABL frequently precede imatinib-based therapy and give rise to relapse in patients with de novo Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL)

Acquired imatinib resistance in advanced Philadelphia-positive acute lymphoblastic leukemia (Ph(+) ALL) has been associated with mutations in the kinase domain (KD) of BCR-ABL. We examined the prevalence of KD mutations in newly diagnosed and imatinib-naive Ph(+) ALL patients and assessed their clinical relevance in the setting of uniform frontline therapy with imatinib in combination with chemotherapy. Patients enrolled in the German Multicenter Study Group for Adult Acute Lymphoblastic Leukemia (GMALL) trial ADE10 for newly diagnosed elderly Ph(+) ALL were retrospectively examined for the presence of BCR-ABL KD mutations by denaturing high-performance liquid chromatography (D-HPLC), cDNA sequencing, and allele-specific polymerase chain reaction (PCR). A KD mutation was detected in a minor subpopulation of leukemic cells in 40% of newly diagnosed and imatinib-naive patients. At relapse, the dominant cell clone harbored an identical mutation in 90% of cases, the overall prevalence of mutations at relapse was 80%. P-loop mutations predominated and were not associated with an inferior hematologic or molecular remission rate or shorter remission duration compared with unmutated BCR-ABL. BCR-ABL mutations conferring high-level imatinib resistance are present in a substantial proportion of patients with de novo Ph(+) ALL and eventually give rise to relapse. This provides a rationale for the frontline use of kinase inhibitors active against these BCR-ABL mutants.

Philadelphia chromosome-positive acute lymphoblastic leukemia: impact of imatinib treatment on remission induction and allogeneic stem cell transplantation

Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) has been associated with the worst patient survival rates of the various acute leukemias. Imatinib mesylate is a novel therapeutic agent that targets the BCR-ABL tyrosine kinase, the molecular abnormality associated with Ph+ ALL. The combination of imatinib with chemotherapy has led to improved and durable treatment responses in adult patients with Ph+ ALL, including the elderly population. Hematopoietic stem cell transplantation has also integrated imatinib into its transplant strategies, with early data suggesting improved progression-free survival without clearly identifiable augmented toxicity. Second-generation tyrosine kinase inhibitors offer potentially even greater improvements on these excellent imatinib-associated outcomes. This review addresses the evolution of the management of Ph+ ALL and is intended to assist in the description of its new natural history.

Management of acute lymphoblastic leukemia in older patients

Although the median age for adults with acute lymphoblastic leukemia (ALL) is older than 60 years, relatively few of these patients have been enrolled on prospective clinical trials. The presence of coexisting medical disorders and unfavorable cytogenetic and biologic disease characteristics within this population presents considerable challenges for successful treatment using conventional chemotherapy programs. Selected patients have achieved remission and long-term survival following intensive chemotherapy. Philadelphia (Ph) chromosome (BCR/ABL)-positive ALL is particularly common among older patients. The availability of specific tyrosine kinase inhibitors is changing the prognosis for this challenging subset.

Autologous stem cell transplant in ALL: who should we be transplanting in first remission?

Long-term disease-free survival (DFS) has been reported after autologous stem cell transplantation for acute lymphoblastic leukemia. Phase II studies have evaluated its role in first and subsequent complete remission (CR) with DFS rates of up to 50%. It has been under-utilized in 1st CR in part, due to a concern that patients who relapse after autologous stem cell transplantation (ASCT) have fewer options for salvage treatment of relapsed disease. Unfortunately, survival rates of <5% are reported in patients who relapse, regardless of initial therapy. Few prospective, randomized trials have analyzed large enough numbers of patients to allow us to determine the appropriate patient population for autologous transplantation. Although variability in the available studies makes it difficult to draw a definite conclusion, and many issues remain unresolved, available data suggests that there may be a group of patients for whom ASCT in first remission is a reasonable and perhaps superior treatment choice. Factors such as risk features at diagnosis, and minimal residual disease following induction therapy greatly affect outcome following ASCT. The available data as well as the questions that remain to be answered will be discussed and reviewed.

Imatinib therapy prior to myeloablative allogeneic stem cell transplantation

It is unknown whether imatinib prior to myeloablative haematopoietic stem cell transplantation (HSCT) increases transplant-related toxicity. Among the side effects induced by imatinib, myelosuppression and liver injury might worsen HSCT outcomes. We retrospectively analysed engraftment, liver toxicity, acute graft-versus-host disease (aGVHD) incidence and 100-day mortality in 30 patients with BCR/ABL-positive leukaemias who received imatinib before HSCT and compared results of 48 age-matched controls who did not receive preceding imatinib. Both neutrophil and platelet engraftment occurred more rapidly among imatinib patients but the differences adjusted for Gratwohl scale were not statistically significant (P = 0.18 and 0.22, respectively). The adjusted hazards of having liver function tests (LFTs) >1.5 normal increased and the adjusted durations of elevated LFTs were not significantly different. The estimated adjusted difference in mean peak bilirubin values was also not significantly different (P = 0.48). However, the adjusted hazard of increased creatinine >1.5 normal was significantly higher in the imatinib group (HR = 4.09, P = 0.02). The adjusted odds of grades II-IV aGVHD were similar in both groups (OR = 0.86, P = 0.78), and while the adjusted odds of 100-day mortality were lower among imatinib patients, the difference was not significant (OR = 0.65, P = 0.60). These data do not provide any evidence that imatinib preceding HSCT increases acute transplant-related toxicities.

Philadelphia positive acute lymphoblastic leukaemia of childhood

On current chemotherapeutic regimens, children with Philadelphia positive acute lymphoblastic leukaemia show a heterogeneous response to treatment. A few respond quickly to treatment and achieve long-term remission. Some fail to achieve remission after induction and the majority respond slowly to treatment. Relapse on treatment is common and remission is sustained in a proportion of cases only after allogeneic stem cell transplantation (allo-SCT). The use of imatinib along with conventional cytoreductive therapy, prior to allo-SCT appears to be the most promising strategy. The future lies in the molecular evaluation of response to treatment and combination targeted chemotherapy.

Early molecular response to posttransplantation imatinib determines outcome in MRD+ Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL)

In adult Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL), minimal residual disease (MRD) after stem cell transplantation (SCT) is associated with a relapse probability exceeding 90%. Starting imatinib in the setting of MRD may decrease this high relapse rate. In this prospective multicenter study, 27 Ph+ ALL patients received imatinib upon detection of MRD after SCT. Bcr-abl transcripts became undetectable in 14 (52%) of 27 patients, after a median of 1.5 months (0.9-3.7 months) ((early)CR(mol)). All patients who achieved an (early)CR(mol) remained in remission for the duration of imatinib treatment; 3 patients relapsed after imatinib was discontinued. Failure to achieve polymerase chain reaction (PCR) negativity shortly after starting imatinib predicted relapse, which occurred in 12 (92%) of 13 patients after a median of 3 months. Disease-free survival (DFS) in (early)CR(mol) patients is 91% +/- 9% and 54% +/- 21% after 12 and 24 months, respectively, compared with 8% +/- 7% after 12 months in patients remaining MRD+ (P < .001). In conclusion, approximately half of patients with Ph+ ALL receiving imatinib for MRD positivity after SCT experience prolonged DFS, which can be anticipated by the rapid achievement of a molecular complete remission (CR). Continued detection of bcr-abl transcripts after 2 to 3 months on imatinib identifies patients who will ultimately experience relapse and in whom additional or alternative antileukemic treatment should be initiated.

The effect of first-line imatinib interim therapy on the outcome of allogeneic stem cell transplantation in adults with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia

Previously, we suggested that imatinib incorporation into conventional chemotherapy as an alternative (imatinib interim therapy) might be a useful strategy for bridging the time to allogeneic stem cell transplantation (SCT) for newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL). Here, we provide an updated report on this strategy in 29 patients. At the time of enrollment, 23 patients (79.3%) achieved complete remission (CR). After the first imatinib cycle, the median breakpoint cluster region-Abelson oncogene locus (BCR-ABL)/ABL ratios decreased by 0.77 log in 25 (86.2%) responders, and their BCR-ABL/ABL ratios decreased further by 0.34 log after the second imatinib cycle, which included 7 molecular CR. One patient (4.3%) relapsed during the imatinib therapy. The remaining 3 patients were primarily refractory to both imatinib and chemotherapy. Twenty-five (86.2%) of the 29 patients received transplants in first CR. With a median follow-up duration of 25 months after SCT, the 3-year estimated probabilities of relapse, nonrelapse mortality, disease-free survival, and overall survival were 3.8%, 18.7%, 78.1%, and 78.1%, respectively. In comparison to our historical control data, first-line imatinib interim therapy appears to provide a good quality of CR and a survival advantage for patients with Ph(+) ALL. Further long-term follow-up is needed to validate the results of this study.

Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia

Philadelphia chromosome positive (Ph(+)) acute lymphoblastic leukemia (ALL) includes at least one-quarter of all adults with ALL. Until recently, conventional chemotherapy programs that have been effective in other precursor B-cell ALL cases have been unable to cure patients with this diagnosis. Allogeneic stem cell transplantation early in first remission has been the recommended therapy. The availability of imatinib mesylate and other tyrosine kinase inhibitors and small molecules that affect the BCR/ABL signaling pathways may be changing the treatment paradigm and the prognosis for these patients. The results from clinical trials using imatinib in the frontline setting and in relapsed patients as well as preliminary experience treating imatinib-resistant Ph(+) ALL will be described.