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Sustained Complete Molecular Remissions After Treatment With Imatinib-Mesylate in Patients With Failure After Allogeneic Stem Cell Transplantation for Chronic Myelogenous Leukemia: Results of a Prospective Phase II Open-Label Multicenter Study

From the III. Med. Klinik, Johannes Gutenberg-University, Mainz; University of Ulm, II. Med. Klinik, Charité; Humboldt University, Berlin; Deutsche Klinik für Diagnostik Wiesbaden, University of Munich, University of Frankfurt, University of Düsseldorf, University of Dresden, University of Heidelberg at Mannheim, Novartis AG, Nürnberg, Germany

Address reprint requests to address: Thomas Fischer III, MD. Department of Medicine, Johannes Gutenberg-University, Langenbeckstr. 1, 55131 Mainz, Germany; e-mail: t.fischer{at}3-med.klinik.uni-mainz.de

	ABSTRACT

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
PURPOSE: In the era of molecular therapy of chronic myelogenous leukemia (CML) applying BCR-ABL tyrosine kinase inhibitors, the usefulness of molecular end points, in particular, quantitative polymerase chain reaction (PCR) for BCR-ABL in monitoring responses has been broadly accepted. Therefore, we have designed a prospective phase II trial in CML, which, for the first time, evaluated the feasibility and safety of molecular end points as surrogate markers to guide through a stratified treatment algorithm within a multicenter trial.

PATIENTS AND METHODS: As a clinical model, we adopted minimal residual disease (MRD) found in relapse after allogeneic stem cell transplantation (SCT) in CML. Forty-four patients were enrolled and received the BCR-ABL tyrosine kinase inhibitor imatinib (IM) at a starting dose of 400 mg/d. The quality of molecular responses achieved then decided on discontinuation of IM or dose escalation up to 800 mg/d, and finally, on application of donor lymphocyte infusions.

RESULTS: Seventy percent of patients achieved a complete molecular response (CMR), defined as nested PCR-negativity for BCR-ABL in three consecutive samples. Interestingly, in four out of 10 patients who discontinued IM, CMR was durable even after cessation of IM with a median follow-up of 494 days. This suggests the possibility of long-term tumor control in a subset of patients.

CONCLUSION: The treatment strategy showed that IM treatment was well-tolerated and highly efficacious in MRD after allogeneic SCT. Moreover, this study demonstrated that evaluation of a molecular end point within a multicenter trial can be a safe and effective tool for clinical decision making.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
Chronic myelogenous leukemia (CML) is a myeloproliferative disease, characterized by an initial indolent chronic phase (CP), followed by an advanced accelerated phase (AP) and an advanced blastic phase (BC). The reciprocal chromosomal translocation t (9;22)(q34;q11) results in the production of the chimeric protein BCR-ABL, which is the molecular hallmark of this disease.^1-3 BCR-ABL is a constitutively-activated tyrosine kinase, leading to continuous cell proliferation, inhibition of apoptosis, and deregulation of cellular adhesion.⁴ For more than 20 years, allogeneic bone marrow (BM) or peripheral blood stem cell transplantation represented the only curative treatment for CML.^5,6 Graft-versus-leukemia (GvL) effects contribute substantially to the curative potential of this approach.^7,8 However, relapse occurs in approximately 5% to 20% of patients transplanted in CP. While some patients remain in a stable minimal residual disease (MRD) status, others rapidly progress to overt clinical relapse.⁹ Because of the potential to re-induce molecular remissions by augmenting or re-establishing the GvL effect, cessation of immunosuppression¹⁰ and, particularly, donor lymphocyte infusion (DLI) are standard of care in patients with relapse after allogeneic stem cell transplantation (SCT). However, this approach is frequently associated with substantial risks, mainly induction of graft-versus-host disease (GvHD) or BM suppression,^11-12131415 which in large surveys are observed in approximately 48% and 18% of patients.¹⁶

Recently, imatinib-mesylate (IM) has been introduced in CML therapy. The drug acts by blocking the adenosine 5'-triphosphate-binding site of BCR-ABL, platelet-derived growth-factor receptor, and c-Kit receptor. It induces growth arrest in vitro and/or apoptosis in BCR-ABL expressing cells.^17-1819 The initial clinical phase I –II trials showed a high rate of hematologic and cytogenetic responses in CP patients after interferon (IFN) failure and in AP and BC.^20-22 More recent studies established IM as standard first line treatment for patients with CML in CP, at least with a low or intermediate risk profile.²³

The potential side effects of DLI make IM a highly attractive candidate for the treatment of patients with relapse after allogeneic SCT, in particular, in early molecular relapse. IM may help to postpone DLI in patients in poor condition or at high risk for aggravation of GvHD. Suppression of residual disease could re-establish complete chimerism and restore full GvL effects. Previous data already demonstrated some clinical efficacy in this indication.^24-2526 However, as these studies were retrospectively evaluated, only limited information on the true feasibility and efficacy of this approach was available. Moreover, there was only little information on the rates, quality, and durability of molecular responses, which was additionally hampered by the lack of a standardized polymerase chain reaction (PCR) protocol.²⁵ As there is increasing evidence that real time quantitative PCR (RT-Q PCR) for BCR-ABL is a powerful tool to monitor responses to IM, we designed a prospective multicenter phase II trial that included close monitoring of MRD, using central laboratory-based RT-Q PCR and qualitative nested real time PCR (RT-PCR), to evaluate the rate of molecular responses.²⁷ Moreover, we incorporated molecular end points as decision points in a stratified treatment algorithm that included discontinuation of IM, dose escalation of IM, and/or application of DLIs. Our goal was to test whether this approach was feasible and safe within a multicenter trial. In addition, we speculated that treatment of patients in a MRD situation with IM may help to re-establish GvL control and may re-induce durable complete molecular response (CMR). Finally, we wanted to test whether discontinuation of IM was feasible once CMR was re-established.

	PATIENTS AND METHODS

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
Study Design
The study was performed as a prospective phase II, multicenter, open-label, nonrandomized trial, which was performed in accordance with the Declaration of Helsinki and had been approved by the ethics committees of the participating centers.

Patients
Patients in CP before allogeneic SCT were divided into two groups. Group A: Patients with molecular relapse, defined as conversion to BCR-ABL PCR-positivity for at least two consecutive samples as evaluated by nested PCR at the primary site or increase of BCR-ABL/G6PDH ratio of more than one log as evaluated by Q PCR. Group B: Patients with cytogenetic relapse after allogeneic SCT. Patients transplanted in CML AP or BC were, because of the low number enrolled (n = 5), only included for the safety analysis.

Inclusion Criteria
CML patients after allogeneic SCT, 18 years of age, with detectable BCR-ABL transcripts with fusions corresponding to the P190 or P210 hybrid proteins as evaluated by RT-PCR or positive cytogenetics for the Ph-chromosome were included. Patients must also have an Eastern Cooperative Oncology Group score 2, AST and ALT not more than 3x the upper normal limit (UNL, 5x UNL for patients with GvHD of the liver), total serum bilirubin level not more than two times UNL (three times UNL for GvHD), serum creatinine concentration not more than 2.5x UNL, and a negative pregnancy test before the initiation of study drug, if applicable. Barrier contraceptive precautions had to be used throughout the trial in either sex. Patients were also required to supply written, voluntary informed consent before study entry.

Exclusion Criteria
Patients relapsing in AP or BC were excluded. Patients after allogeneic transplantation previously treated for relapse with DLI within 6 months of day 1 were also excluded. Patients receiving interferon-alfa, cytarabine, busulfan, hydroxyurea, or other investigational agents within 28 days for relapse after allogeneic transplantation and severe concomitant medical diseases were also excluded.

Treatment Schedule
If medically acceptable, immunosuppressive therapy had to be tapered first before inclusion in this trial (Fig 1). Patients not achieving a CMR (defined as negative nested RT-PCR for BCR-ABL) after a period of 2 months, or patients who were unable to tolerate cessation of immunosuppressives, received IM at a starting dose of 400 mg/d. Patients, already off immunosuppressive therapy directly started with IM. Molecular monitoring and definitions of response are described below. In case patients did not achieve at least a major molecular response (MMR) after 3 months, IM dose was increased to 600 mg/d to 800 mg/d. If patients did not achieve a CMR after a maximum of 9 months, DLI could be used. The decision which DLI-schedule and which T-cell dose should be used were left to the discretion of the transplant center. With regard to cessation of IM, the following standard was required as per trial protocol: patients had to be treated with IM for at least 6 months and had to be in CMR as defined by negative nested PCR at three consecutive time points within a period of 3 months. When both requirements were fulfilled, cessation of IM was allowed per protocol. At the end of the study period an additional extended follow-up was initiated.

View larger version (6K): [in this window] [in a new window]   Fig 1. Overall treatment plan. After initial treatment with imatinib (IM) using 400 mg/d, dose escalation was planed in patients without complete molecular response (CMR). After 9 months of IM therapy, donor lymphocyte infusion (DLI) treatment was optional. In patients achieving CMR, cessation of study drug was foreseen, by discretion of the treating physician. CP, chronic phase; CML, chronic myelogenous leukemia; s.p., status post; SCT, stem cell transplantation; MMR, partial molecular response.

Diagnostic Procedures
BM aspiration was performed before initiation of treatment and every 3 months. Analyses included cytology, BM, and/or peripheral blood (PB) chimerism analysis and a two-step RT-PCR procedure. Samples of PB were collected every 4 weeks for chimerism analysis and RT-PCR. Analyses of BM cytology, histology, and BM and PB chimerism were performed at the local centers according to local guidelines. Cytogenetic response was based on the prevalence of Ph-positive metaphases among at least 20 metaphase cells in each BM sample and was defined as complete (0% Ph-positive cells), partial (1% to 35%), minor (36% to 95%), or none (>95%).^19,21 Complete chimerism was judged in case of detection of more than 95% donor type, with the methods used in the particular institutions.

Molecular Analysis
Patients with isolated molecular relapse had to be tested PCR-positive for BCR-ABL for two consecutive samples at the local centers before enrollment. Baseline and follow-up samples were analyzed on a 4-week (PB) or 3-month (BM) basis within the study period of 9 months. Thereafter, follow-up samples were collected on a 2 month to 3 month basis. To avoid variations in methodology (RNA extraction, PCR assays), these analyses were performed centralized as a two-step procedure. Samples were sent via express mail, which allowed arrival at the lab within 24 hours for the majority of samples. This has been proven previously as a reliable method.²⁷

Quantitative PCR: RT-Q PCR was performed using a commercially available RT-Q PCR assay applying hybridization probes and detection on the LightCycler device (Roche, Mannheim, Germany; catalogue number 2207206). This assay contains material for reverse transcription using oligohexamer primer, as well as primers and probes for the detection of BCR-ABL and G6PDH. Additional positive and negative control RNA for both genes is also provided. A standard dilution of RNA for the detection of G6PDH allows control of the assay performance. Samples are analyzed for both genes within a single run in separate capillaries. Results of the amplification of both genes are used to express a ratio of the expression of BCR-ABL levels relative to G6PDH-levels (ratio of copy number BCR-ABL/copy number G6PDH)^28,29,32. Extensive pretesting and quality round results revealed a sensitivity of 1:10⁴ in patient samples with appropriate quality of RNA. In our experience, this can be considered to be present in a given sample, if G6PDH can be detected within 30 Q PCR cycles. In any case, if sample quality was insufficient, only positive results have been taken into account for reporting results obtained by quantitative or nested PCR. Experiments to test for measurement reliability revealed the following results in repetitive analyses of samples with high, medium-low (approximately two log reduction), and low (approximately three log reduction) BCR-ABL/G6PDH levels: mean, 24.57; SD, 2.43 and coefficient of variation (CV) 9.89; mean, 0.0706; SD, 0.0147; CV, 20.88; mean, 0.0173; SD, 0.0063; CV, 36.41 (data not shown). Thus, measurement reliability is comparable to results obtained by others.³⁰ However, in contrast to CP patients, several factors may influence the results of Q PCR in our patient population, with the majority of patients presenting with low levels of baseline tumor load: shipping,storage, slight variances in chemicals over a 3-year period, fluctuating cytopenias because of antiviral therapy, infection, and effects of GvHD. Therefore, for the purpose of this study, we defined a true change in MRD level as a 10-fold or greater increase/decrease in BCR-ABL/G6PDH levels to take these variables into account. This had to be confirmed by two consecutive Q PCR analyses to strictly avoid overscoring the clinical relevance of a single PCR result. This threshold for a significant change in BCR-ABL levels was adopted solely for the purpose of this trial and we acknowledge that in other trials investigating different patient populations a lower threshold of significance of Q PCR changes has been validly implemented.³⁰

To monitor the entire workflow stability over the more than 36-month trial period, repetitive aliquots (n = 36) from a control patient sample were analyzed during this period. With a mean of 9.79 BCR-ABL/G6PDH results varied from 2.13 to 26.98, which reflects a SD of 5.88. Thus, the two SD range corresponds to approximately one log and provides an estimate of measurement reliability at the 95% level of confidence for the controls, and basically, confirmed our results obtained in pretesting before the trial.

Because of the limitation of material and because of the large number of samples analyzed, we did not perform replicate Q PCR analysis in a given patient sample in general. However, nested PCR always was performed as duplicate analysis with adequate positive and negative controls. In addition, disease course was closely monitored. For example, in case of increase in BCR-ABL levels for two log or more in comparison to the last sample analyzed or in case of negative Q PCR on prior positive samples, Q PCR and/or nested PCR was repeated. More than 100 samples were re-analyzed this way. In only eight of these patient samples (all were characterized by very low copy numbers of BCR-ABL mRNA), results needed to be corrected by reporting the result with the higher value to avoid overscoring the significance of a single Q PCR result.

Erythrocyte lysis was performed in BM or PB samples and in general 5 x 10⁵-1 x 10⁶ cells were used for RNA extraction using the HighPure RNA extraction kit (Roche, Mannheim, Germany; catalogue number 1828665). For Q PCR, an amount of 800 ng RNA was used for cDNA synthesis, if ever available, in a final volume of 20 µL, of which, 10 µL was used for Q PCR.

Nested PCR: In case of Q PCR negativity, nested PCR was performed, with a sensitivity of about 1:10⁵ to 1:10⁶ as described before.³¹ Reverse transcription was performed on a separate aliquot of RNA to minimize the risk of cross contamination. The Titan One Tube PCR System (Roche, Mannheim, Germany; catalogue number 1855476) was used with first round PCR primers for reaction initiation in a final volume of 25 µL. This system allows direct performance of first round PCR within the same tube after completion of reverse transcription, followed by nested PCR, using 2 µL of the product. PCR reactions were performed on an Eppendorf Thermal Cycler (Eppendorf, Hamburg, Germany), and products were subsequently analyzed by gel electrophoresis on 2% agarose gels. For each sample, ABL was analyzed as a control reaction and all nested PCR analyses were performed in duplicate.

In case of discrepancy between PCR results of matched BM or PB samples collected on the same day, the result with the higher level of BCR-ABL was reported. However, in the vast majority of pairs analyzed, BM and PB MRD levels did not differ significantly. Together, with ongoing follow-up, a total of more than 700 samples have been analyzed by Q PCR and nested PCR during the course of this trial.

Definitions of Molecular Response
For the purpose of this study, CMR was defined as negative nested PCR for BCR-ABL in three consecutive samples after initial PCR positivity. MMR was defined as the reduction of BCR-ABL/G6PDH ratio of at least one log or conversion to Q PCR negativity in case of low initial MRD levels in three consecutive samples. This definition differs from previously used definitions owing to the already lower BCR-ABL transcript levels found in the population included in this trial. Stable molecular disease was defined as BCR-ABL/G6PDH-levels within one log of baseline levels determined in three consecutive samples. Rising BCR-ABL levels were defined as either an increase of at least two logs in comparison to baseline levels in two consecutive Q PCR results over a period of 2 months or an increase of at least one log in three consecutive Q PCR results over a period of 3 months. Unsatisfactory therapeutic effect was defined as a stable PCR or rising Q PCR results for patients who had not achieved any remission during the treatment course.

For patients with any response, molecular relapse/progression was defined as reconversion to BCR-ABL-positivity in case of CMR or the increase of more than one log for the BCR-ABL/G6PDH ratio for patients with MMR in three consecutive samples (PB or BM).^32-35

Duration of Molecular Response
Remission duration was the time from first documentation of molecular and hematologic response to death or relapse, whichever came first.

	RESULTS

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
Patients
Forty-four patients were enrolled into the study. Thirty-seven patients were in CP before SCT, 18 of those patients had molecular relapse (Group A) and 19 patients had cytogenetic relapse (Group B) before the start of IM. Five patients were in AP/BC before SCT and were included for safety analysis only. Two patients were excluded from analysis, one because of protocol violation (BC at study entry) and the other because of lack of follow-up samples. Demographic/disease-specific data for the patient groups are summarized in Table 1. In brief, in both groups (A, B) there were no apparent differences in age at diagnosis (median, 37 years), time from initial diagnosis to allogeneic SCT (median, 3.5 years), time from SCT to start of IM (median, 2.1 years), and Eastern Cooperative Oncology Group scores at inclusion (median, 0), respectively. The majority of patients (78.4%) had been transplanted during the first CP and acute/chronic GvHD had occurred in 56.8% and 27% of patients, respectively. Best response to SCT had been CMR in 67.6%, cytogenetic CR in 21.6%, and inferior or unknown response in 10.8% of patients included in groups A and B (Table 1).

Focusing on the results of the more sensitive molecular analysis, a CMR was achieved in 62.2% of assessable patients (23 out of 37 patients). Thus, in these patients, the residual disease levels declined below the detection limit of all methods used. When results were analyzed separately for Group A and Group B patients, then the CMR rates were 77.8% (14 of 18 patients) and 47.4% (9 out of 19 patients), respectively. Median times to response were 28 days and 114 days, respectively. Of the remaining patients, six out of 37 patients (16.2%) achieved MMR and at this time point eight out of 37 patients (21.6%) had an unsatisfactory therapeutic effect in terms of stable BCR-ABL/G6PDH levels.

Analysis of chimerism was performed separately for PB and BM. In Group A, results were available from PB in 15 patients. Seven patients presented with complete chimerism at baseline, and from the remaining patients, seven out of eight showed complete chimerism at least at one time point during the study phase. Corresponding figures for Group B are nine assessable patients with three patients in complete chimerism at baseline. One out of six patients from the remaining patients converted to complete chimerism during the study phase. This results in a rate in complete chimerism of 14 out of 15 patients in Group A (93.3%) and four out of nine patients in Group B (44.4%, P < .015). Results PB of BM analysis are summarized in Table 4.

At the time of this analysis, 15 out of 37 patients had lost their best molecular response at any time during the treatment: Group A: three patients while continuing IM, four patients after cessation of the study drug, Group B: six patients while continuing IM, two patients after cessation of the study drug. However, as the majority of assessable patients regained CMR on re-initiation of IM (two out of two assessable patients with CMR) or DLI (four out of six assessable patients CMR, two out of six assessable patients MMR) this figure underestimates the number of patients with prolonged benefit (six patients had no follow-up and one patient was not assessable). At the time of this analysis, only two patients developed hematologic relapse (one patient CP, one patient BC). The overall survival rate of Group A and Group B patients (n = 37) was 100% at a median follow-up of 595 days for the entire cohort. However, one patient died on day 649 (Group A) as a result of progression of leukemia.

Duration of CMR After Cessation of IM and Re-Initiation of Therapy
One of two patients, in whom IM was stopped because of an adverse event at day +111 developed CMR without re-initiation of IM and with no signs of relapse as evaluated up to day +684 (Fig 3A). IM was stopped in CMR during follow-up in six patients of Group A and in five patients of Group B. Follow-up data are available from nine patients: six patients lost CMR; however, interestingly, three patients (Group A: one patient, Group B: two patients) demonstrated stable CMR after cessation of the study drug, now lasting for +375, +456, and +532 days after withdrawal (Fig 3B-D). Together with the patient, who stopped IM because of an adverse event and now is in CMR for +573 days after withdrawal of IM, this resulted in four out of 10 assessable patients (40%) with sustained complete molecular response after cessation of IM.

View larger version (13K): [in this window] [in a new window]   Fig 3. Depicted are all patients (A-D) with stable complete molecular response (CMR) after cessation of imatinib (IM). (A) In this patient, IM was stopped due to an adverse event; however, he converted to stable CMR. (D) For the third sample analyzed, only nested polymerase chain reaction was informative and has been depicted separately. (*) IM dosing information. qPCR, quantitative polymerase chain reaction.

Of the six patients who lost CMR, a second CMR was achievable by IM or DLI in each patient. In the remaining four patients, at the time point of this analysis the following responses were observed: one patient with MMR characterized by nested PCR- positivity on IM, one patient with intermittent positive nested PCR results, and one patient with rising BCR-ABL levels on a watch and wait strategy, respectively, and one patient with no follow-up data.

Donor Lymphocyte Infusions
Altogether, DLI have been given to seven patients who did not achieve CMR or relapsed. All of these patients had been in their first CP at the time of SCT, and four patients had a matched related donor. A history of GvHD had been present in all patients (five acute GvHD, four chronic GvHD). Patients received one to two doses of T-cells (total T-cell dose 1 x 10⁶ to 11.4 x 10⁷/kgbw). Four patients achieved CMR (Fig 4), two patients had MMR, and in one patient response was not assessable. One patient reported a reactivation of GvHD. This event was mild to moderate and was steroid responsive.

View larger version (5K): [in this window] [in a new window]   Fig 4. This patient (25-A-13) achieved a complete molecular remission on treatment with imatinib (IM); however, he experienced relapse even after increase of the IM dose. Therefore, he recieved DLI (1 x 106/kg body weight) and this resulted in rapid induction of CMR, which is ongoing for more than 1 year. (*), IM dosing information. qPCR, quantitative polymerase chain reaction.

	DISCUSSION

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

Prospective monitoring of safety and feasibility of IM revealed a low number of grade 3 or 4 events, which were comparable to prior experiences with IM.³⁶ In particular, the rate of hematologic toxicities has been acceptable, with a low number of dose modifications. Of note, only a single and mild reactivation of GvHD was observed. This compares favorably with the experience using DLI, in which up to 50% of patients experience an episode of acute or chronic GvHD, which may lead to disability or even death.¹⁶

Therapeutic efficacy was evaluated with a clear focus on the results of molecular analysis. The procedure used had a failure rate of less than 3% of samples not suitable for analysis within this multicenter trial. Results were obtained in a blinded fashion, as information of the clinical course was not available for the centralized laboratory during the study. After comparing results with treatment course and dose interruptions/reductions, changes in BCR-ABL levels corresponded excellently with the clinical disease course (Fig 2A).

View larger version (20K): [in this window] [in a new window]   Fig 2. Example of a patient with fluctuating BCR-ABL/G6PDH levels because of dosing errors ('), which resolved during continuing treatment. qPCR, quantitative polymerase chain reaction.

Comparing this study to the recent work of Kantarjian et al,²⁴ there are major differences concerning patient selection and response monitoring. Kantarjian et al included a heterogeneous population of patients, with various pretreatments for relapse, including DLI in 13 out of 28 patients. Overall, there was a complete hematologic response rate of 74%, and the CCR rate was 35%. GvHD occurred in five out of 28 patients, which differs significantly from our results, suggesting the influence of preceding DLI-therapy. Olavarria et al²⁵ reported on a European Bone Marrow Transplantation Group retrospective survey of 128 patients with relapsed CML in various phases after SCT. CCR rates were 58% for CP, 48% for AP, and 22% for BC. Rates of molecular remissions are not comparable to our report as results of nested PCR and Q PCR were pooled and information on the sensitivity of PCR results is not available. Recently, DeAngelo at al²⁶ reported on their experience of the extended use of IM in a small series of patients with relapse after allogeneic SCT. CP-CML patients in cytogenetic relapse received daily doses of 400 mg to 600 mg of IM. Nine out of 10 patients did develop CCR, and seven out of 10 patients converted to nested PCR negativity after 14 months of treatment. In contrast to our series, in which a closer molecular follow-up was included, no relapses of responding patients were observed. However, as none of the patients stopped IM treatment during follow-up, induction of IM-independent control of leukemia has not been addressed within that study.

Several conclusions can be drawn from our results. First and most important, we show that the concept of re-establishing control of leukemia by using IM in MRD is valid. With ongoing complete chimerism, GvL effects may be augmented and, therefore, at some time point cure, in terms of permanent tumor control, may be achieved. Increasing CMR rates on ongoing treatment and the stability of CMR in some patients for more than 1 year after cessation of IM support this concept.

The low toxicity profile of IM observed in this indication allows the treatment of early occurrence of molecular relapse without putting the patient at risk for induction of GvHD or BM aplasia, which in the past has hampered the use of DLI until frank relapse. The trend to an earlier (28 days v 114 days) response and higher overall rate of CMR (83.3% v 57.9%) in Group A patients encourages this approach. At study initiation, there was some concern to expose this patient population to higher doses of IM. Therefore, we have chosen a careful strategy. Now, with our favorable safety data available, a more aggressive dosing schedule (600 mg/d to 800 mg/d) may be justified and may help to further optimize results, as demonstrated for high-dose IM in CP-CML.³⁸ On the other hand, this trial also shows that discontinuation of IM in CMR should not be attempted too early: There was a trend for longer pretreatment in patients with continuous CMR after cessation of IM in comparison with patients with no sustained responses (median, 269 days v 151 days). Therefore, it can be speculated, that suppression of the malignant clone has to be sufficiently long to allow GvL effects to finally control residual leukemia.

A monitoring strategy using Q PCR plus nested PCR, as described here, is an excellent and reliable tool for surveillance of patients. This allows an upfront attempt to re-induce CMR with IM and to postpone DLI. However, we believe that DLIs will continue to have an important role in management of relapse after SCT, and that a combined-modality approach of IM with DLI in a sequential schedule should be explored further. As to the optimal time point, one may envision that DLI therapy is most safely and most efficaciously applied when the following prerequisites are given: achievement of complete or nearly complete donor chimerism and molecular response and absence of active GvHD. On the basis of the high-risk profile of patients transplanted in second CP or in AP/BC, we believe that this patient group will continue to benefit from DLI therapy. However, early initiation of antileukemic therapy, using a short course of IM, may help to improve treatment results in this high-risk group.

In patients transplanted in first CP, it is currently difficult to give general recommendations as to the selection criteria for patients going on to receive DLI. Certainly, it appears reasonable to treat all patients not achieving CMR on IM with DLI. Data of this trial also suggest that it may be safe to postpone DLI until relapse or resistance at a molecular level is evident. This could be advantageous in a high-risk situation (ie, significant GvHD, mismatch SCT). However, we believe that these questions need to be addressed within a randomized phase III trial. This trial may also investigate whether patients achieving stable CMR may discontinue IM.

Taken together, we conclude that IM treatment is safe and highly efficacious in patients with relapse after SCT for CP-CML. Implementation of molecular end points within a multicenter clinical trial has proved to be feasible and safe in clinical decision making. We believe that this is important information for the design of future clinical trials using second generation BCR-ABL tyrosine kinase inhibitors as BMS-354825 or AMN-107.^39,40

	Authors' Disclosures of Potential Conflicts of Interest

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
Although all authors completed the disclosure declaration, the following authors or their immediate family members indicated a financial interest. No conflict exists for drugs or devices used in a study if they are not being evaluated as part of the investigation. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors.

Authors Employment Leadership Consultant Stock Honoraria Research Funds Testimony Other Georg R. Hess Novartis (B) Martin Bornhäuser Novartis (B) Andreas Hochhaus Novartis (A) Novartis (A) Ulrike Haus Novartis Harald Gschaidmeier Novartis Christoph Huber Novartis (A) Novartis (A) Novartis (C) Thomas Fischer Novartis (A) Novartis (A)

Dollar Amount Codes (A) < $10,000 (B) $10,000-99,999 (C) $100,000 (N/R) Not Required

	Acknowledgment

 
We thank study physicians and nurses at the participating centers for their excellent support. We would also like to acknowledge B. Schuch and C. Pietzsch for excellent technical assistance and R. Hylla, IMEREM, for statistical analysis.

	NOTES

 
Authors' disclosures of potential conflicts of interest are found at the end of this article.

	REFERENCES

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION Authors' Disclosures of... REFERENCES

 
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Submitted January 25, 2005; accepted July 14, 2005.

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