Prognostic and therapeutic implications of minimal residual disease at the time of transplantation in acute leukemia

'Acute myeloid leukemia: a comprehensive review and 2016 update'

Acute myeloid leukemia (AML) is the most common acute leukemia in adults, with an incidence of over 20 000 cases per year in the United States alone. Large chromosomal translocations as well as mutations in the genes involved in hematopoietic proliferation and differentiation result in the accumulation of poorly differentiated myeloid cells. AML is a highly heterogeneous disease; although cases can be stratified into favorable, intermediate and adverse-risk groups based on their cytogenetic profile, prognosis within these categories varies widely. The identification of recurrent genetic mutations, such as FLT3-ITD, NMP1 and CEBPA, has helped refine individual prognosis and guide management. Despite advances in supportive care, the backbone of therapy remains a combination of cytarabine- and anthracycline-based regimens with allogeneic stem cell transplantation for eligible candidates. Elderly patients are often unable to tolerate such regimens, and carry a particularly poor prognosis. Here, we review the major recent advances in the treatment of AML.

[Analyses of outcome and prognostic factors of adult acute myeloid leukemia patients received autologous hematopoietic stem cell transplantation]

OBJECTIVE

To evaluate the outcome of patients with acute myeloid leukemia (AML) received autologous hematopoietic stem cell transplantation (APBSCT) in complete remission (CR), and to study the prognostic factors.

METHODS

55 cases of AML who underwent APBSCT in CR between 2008 and 2014 were retrospectively investigated. Major end points of study included overall survival (OS), disease free survival (DFS), relapse rate and transplantation related mortality.

RESULTS

The median follow-up time was 1 091(20-3 024) days after transplantation. The 3-year OS and DFS rates were 77.1% (95%CI 71.2%-83.8%), 73.7% (95%CI 67.2%-80.3%), respectively. 3-year DFS for patients needed less than 200 days to attain minimal residual disease (MRD) ≤0.03% was significantly higher than that of patients required 200 days or more (88.9% vs 46.9%, P=0.042). 3-year DFS for patients with constant MRD negative 90.0% was greater than that of the remaining group 61.1% , but the difference was insignificant (P=0.090). A multivariate analysis of risk factors for relapse identified days from diagnosis to MRD negative was the only independent factor [RR=0.022 (95% CI 0.001-0.604), P=0.024].

CONCLUSION

The results suggested that most AML patients in CR obtained long-term DFS after APBSCT, and continuous monitoring minimal residual disease could be used to evaluate whether adult AML patients should receive APBSCT or not.

Incorporating measurable ('minimal') residual disease-directed treatment strategies to optimize outcomes in adults with acute myeloid leukemia

Curative-intent therapy leads to complete remissions in many adults with acute myeloid leukemia (AML), but relapse remains common. Numerous studies have unequivocally demonstrated that the persistence of measurable ('minimal') residual disease (MRD) at the submicroscopic level during morphologic remission identifies patients at high risk of disease recurrence and short survival. This association has provided the impetus to customize anti-leukemia therapy based on MRD data, a strategy that is now routinely pursued in acute promyelocytic leukemia (APL). While it is currently uncertain whether this approach will improve outcomes in AML other than APL, randomized studies have validated MRD-based risk-stratified treatment algorithms in acute lymphoblastic leukemia. Here, we review the available studies examining MRD-directed therapy in AML, appraise their strengths and limitations, and discuss avenues for future investigation.

Plasma-derived exosomes in acute myeloid leukemia for detection of minimal residual disease: are we ready?

The recent emergence of plasma-derived exosomes as biomarkers of leukemic relapse has introduced the potential for more sensitive non-invasive monitoring of leukemia patients based on the molecular and genetic analysis of the exosome cargo. In principle, the protein, lipid, miRNA, mRNA or DNA profiles of exosomes in patients' plasma that associate with leukemic relapse can be identified. The diagnostic/prognostic value of these profiles could then be validated in prospective clinical studies. Here, we consider the potential of exosomes to fulfill the role of future biomarkers of minimal residual disease in AML. The rationale for developing exosome-based methodology for minimal residual disease detection is based on promising early observations. However, standards need to be established for evaluating exosome identity, isolation from body fluids, and assessment methods. The rapidly expanding knowledge of the exosome biology suggests that the exosome status as potential biomarkers may become clarified in the near future.

Pre- and post-transplant quantification of measurable ('minimal') residual disease via multiparameter flow cytometry in adult acute myeloid leukemia

Measurable (“minimal”) residual disease (MRD) before or after hematopoietic cell transplantation (HCT) identifies adults with AML at risk of poor outcomes. Here, we studied whether peri-transplant MRD dynamics can refine risk assessment. We analyzed 279 adults receiving myeloablative allogeneic HCT in first or second remission who survived at least 35 days and underwent 10-color multiparametric flow cytometry (MFC) analyses of marrow aspirates before and 28±7 days after transplantation. MFC-detectable MRD before (n=63) or after (n=16) transplantation identified patients with high relapse risk and poor survival. Forty-nine patients cleared MRD with HCT conditioning, whereas 2 patients developed new evidence of disease. The 214 MRD^neg/MRD^neg patients had excellent outcomes, whereas both MRD^neg/MRD^pos patients died within 100 days following transplantation. For patients with pre-HCT MRD, outcomes were poor regardless of post-HCT MRD status, although survival beyond 3 years was observed among the 58 patients with decreasing but not the 7 patients with increasing peri-HCT MRD levels. In multivariable models, pre-HCT but not post-HCT MRD was independently associated with OS and RR. These data indicate that MRD^pos patients before transplantation have a high relapse risk regardless of whether or not they clear MFC-detectable disease with conditioning and should be considered for pre-emptive therapeutic strategies.

Minimal Residual Disease Monitoring in Adult ALL to Determine Therapy

Almost 90 % of children and 50 % of adults with acute lymphoblastic leukemia (ALL) are cured by modern treatment regimens, with significant variations due to several disease- and host-related characteristics. The attainment of an early remission and the avoidance of relapse and treatment-related mortality are the fundamental therapeutic steps. In remission patients, the assessment of the disease response to early intensive therapy through the detection and monitoring of minimal residual disease (MRD) can accurately refine the individual prognosis and is increasingly used to support a risk-oriented treatment strategy. In this way, only the patients with an unfavorable MRD response are preferably selected for allogeneic stem cell transplantation, irrespective of their clinical risk class. This choice spares transplant-related toxicities to MRD responsive cases. Further advancement is expected by integrating the MRD analysis with improved pediatric-type regimens and novel targeting agents for ALL subsets at higher risk of relapse.

Comparable outcomes between autologous and allogeneic transplant for adult acute myeloid leukemia in first CR

Although allogeneic hematopoietic stem cell transplantation from an HLA-matched sibling donor (MSD) is a potentially curative post-remission treatment for adults with acute myeloid leukemia (AML) in their first CR, transplant-related morbidity and mortality remains a major drawback. We retrospectively compared the outcomes of patients who underwent autologous peripheral blood stem cell transplantation (auto-PBSCT; n=375) with those who underwent allogeneic bone marrow transplantation (allo-BMT; n=521) and allo-PBSCT (n=380) from MSDs for adults with AML/CR1, in which propensity score models were used to adjust selection biases among patients, primary physicians and institutions to overcome ambiguity in the patients' background information. Both the multivariate analysis and propensity score models indicated that the leukemia-free survival rate of auto-PBSCT was not significantly different from that of allo-BMT (hazard ratio (HR), 1.23; 95% confidence interval (CI), 0.92 to 1.66; P=0.16) and allo-PBSCT (HR, 1.13; 95% CI, 0.85-1.51; P=0.40). The current results suggest that auto-PBSCT remains a promising alternative treatment for patients with AML/CR1 in the absence of an available MSD.

Should acute myeloid leukemia patients with actionable targets be offered investigational treatment after failing one cycle of standard induction therapy?

PURPOSE OF REVIEW

Therapeutic failure in acute myeloid leukemia remains common. It may be advantageous to identify patients with suboptimal treatment responses early as they may benefit from timely care strategy changes. Here, responses portending failure of standard induction therapy are reviewed and therapeutic options examined, including use of investigational, targeted agents for suitable patients.

RECENT FINDINGS

Patients entering complete remission without minimal residual disease early, that is, with one cycle of standard induction chemotherapy, have a lower relapse risk and live longer than other similarly-treated patients, supporting the proposition of early complete remission without minimal residual disease as a criterion for induction therapy success. Investigational small molecule drugs are appealing for patients who fail standard therapies, but complete remission rates as a single agent are typically modest.

SUMMARY

The relative value of different treatment strategies if a first standard induction therapy cycle fails to produce complete remission is unknown. However, retreatment with the same therapy often leads to complete remission and provides a benchmark against which other approaches should be compared. Addition of investigational small molecule drugs to standard reinduction therapy in patients with actionable targets could offer an attractive therapeutic strategy in this situation that might improve outcomes and facilitate clinical drug testing.

Allogeneic Hematopoietic Cell Transplantation for Acute Myeloid Leukemia: Time to Move Toward a Minimal Residual Disease-Based Definition of Complete Remission?

PURPOSE

Patients with acute myeloid leukemia (AML) who are in morphologic complete remission are typically considered separately from patients with active disease (ie, ≥ 5% marrow blasts by morphology) in treatment algorithms for allogeneic hematopoietic cell transplantation (HCT), which implies distinct outcomes for these two groups. It is well recognized that the presence of minimal residual disease (MRD) at the time of transplantation is associated with adverse post-HCT outcome for those patients in morphologic remission. This effect of pre-HCT MRD prompted us to compare outcomes in consecutive patients in MRD-positive remission with patients with active AML who underwent myeloablative allogeneic HCT at our institution.

PATIENTS AND METHODS

We retrospectively studied 359 consecutive adults with AML who underwent myeloablative allogeneic HCT from a peripheral blood or bone marrow donor between 2006 and 2014. Pre-HCT disease staging included 10-color multiparametric flow cytometry on bone marrow aspirates in all patients. Any level of residual disease was considered to be MRD positive.

RESULTS

Three-year relapse estimates were 67% in 76 patients in MRD-positive morphologic remission and 65% in 48 patients with active AML compared with 22% in 235 patients in MRD-negative remission. Three-year overall survival estimates were 26%, 23%, and 73% in these three groups, respectively. After multivariable adjustment, MRD-negative remission status remained statistically significantly associated with longer overall and progression-free survival as well as lower risk of relapse compared with MRD-positive morphologic remission status or having active disease, with similar outcomes between the latter two groups.

CONCLUSION

The similarities in outcomes between patients in MRD-positive morphologic remission and those with active disease at the time of HCT support the use of treatment algorithms that use MRD- rather than morphology-based disease assessments.

Autologous stem cell transplantation for adult acute leukemia in 2015: time to rethink? Present status and future prospects

The use of autologous stem cell transplantation (ASCT) as consolidation therapy for adult patients with acute leukemia has declined over time. However, multiple randomized studies in the past have reported lower relapse rates after autologous transplantation compared with chemotherapy and lower non-relapse mortality rates compared with allogeneic transplantation. In addition, quality of life of long-term survivors is better after autologous transplantation than after allogeneic transplantation. Further, recent developments may improve outcomes of autograft recipients. These include the use of IV busulfan and the busulfan+melphalan combination, better detection of minimal residual disease (MRD) with molecular biology techniques, the introduction of targeted therapies and post-transplant maintenance therapy. Therefore, ASCT may nowadays be reconsidered for consolidation in the following patients if and when they reach a MRD-negative status: good- and at least intermediate-1 risk acute myelocytic leukemia in first CR, acute promyelocytic leukemia in second CR, Ph-positive acute lymphocytic leukemia. Conversely, patients with MRD-positive status or high-risk leukemia should not be considered for consolidation with ASCT.

How I treat adults with relapsed or refractory Philadelphia chromosome-negative acute lymphoblastic leukemia

The long-term prognosis of adult patients with relapsed Philadelphia chromosome-negative acute lymphoblastic lymphoma (ALL) is poor. Allogeneic stem cell transplant in second remission is the only curative approach and is the goal when feasible. There is no standard chemotherapy regimen for relapsed disease, although a few agents are approved for use in this setting. The bispecific CD19-directed CD3 T-cell engager, blinatumomab, has recently been granted accelerated approval by the US Food and Drug Administration for relapsed or refractory disease of B-cell lineage. For patients with relapsed T-cell ALL, nelarabine is available. Liposomal vincristine is also approved for relapsed disease. When selecting combination chemotherapy salvage options, evaluation of the prior treatment and timing of relapse informs treatment decisions. Monoclonal and cellular investigational therapies are quite promising and should be explored in the appropriate patient.

Sequencing small genomic targets with high efficiency and extreme accuracy

The detection of minority variants in mixed samples requires methods for enrichment and accurate sequencing of small genomic intervals. We describe an efficient approach based on sequential rounds of hybridization with biotinylated oligonucleotides that enables more than 1-million-fold enrichment of genomic regions of interest. In conjunction with error-correcting double-stranded molecular tags, our approach enables the quantification of mutations in individual DNA molecules.

A multigene array for measurable residual disease detection in AML patients undergoing SCT

AML is a diagnosis encompassing a diverse group of myeloid malignancies. Heterogeneous genetic etiology, together with the potential for oligoclonality within the individual patient, have made the identification of a single high-sensitivity marker of disease burden challenging. We developed a multiple gene measurable residual disease (MG-MRD) RQ-PCR array for the high-sensitivity detection of AML, retrospectively tested on 74 patients who underwent allo-SCT at the NHLBI in the period 1994-2012. MG-MRD testing on peripheral blood samples prior to transplantation demonstrated excellent concordance with traditional BM-based evaluation and improved risk stratification for post-transplant relapse and OS outcomes. Pre-SCT assessment by MG-MRD predicted all clinical relapses occurring in the first 100 days after allo-SCT compared with 57% sensitivity using WT1 RQ-PCR alone. Nine patients who were negative for WT1 prior to transplantation were correctly reclassified into a high-risk MG-MRD-positive group, associated with 100% post-transplant mortality. This study provides proof of principle that a multiple gene approach may be superior to the use of WT1 expression alone for AML residual disease detection.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for “prime time”?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a “one size fits all” approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for "prime time"?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a "one size fits all" approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Prognostic impact of minimal residual disease in adult acute lymphoblastic leukemia

SUMMARY 

While adult acute lymphoblastic leukemia (ALL) is curable in 40–50% of the patients, the individual prognosis is rather unpredictable due to associated biological and clinical risk factors. In both B- and T-precursor ALL, minimal residual disease (MRD) represents the most sensitive prognostic marker, useful to support critical treatment decisions, ranging from allogeneic stem cell transplantation in patients with inadequate MRD response to chemotherapy only in MRD responsive ones. This optimized risk-adapted strategy allows to spare transplant-associated morbidity and mortality in patients curable by chemotherapy. Further progress is expected from the integration of the MRD-based strategy with improved pediatric-type regimens and novel targeting agents for discrete ALL subsets. These changes are increasing the cure rate to above 50%.

Number of courses of induction therapy independently predicts outcome after allogeneic transplantation for acute myeloid leukemia in first morphological remission

Whether the number of chemotherapy cycles required to obtain a first morphological remission affects prognosis of patients with acute myeloid leukemia (AML) remains controversial. To clarify how achievement of early remission might influence outcome of allogeneic hematopoietic cell transplantation (HCT), we studied 220 consecutive adults with AML in first morphological remission who underwent transplantation after myeloablative or nonmyeloablative conditioning to investigate how the number of standard- or high-dose induction courses required to achieve remission impacted post-HCT outcome. Three-year estimates of overall survival were 65% (95% confidence interval [CI] 56% to 73%), 56% (95% CI, 43% to 67%), and 23% (95% CI, 6% to 46%) for patients requiring 1 course, 2 courses, or >2 courses of induction therapy; corresponding relapse estimates were 24% (95% CI, 17% to 31%), 43% (95% CI, 31% to 55%), and 58% (95% CI, 30% to 78%), respectively. After covariate adjustment (minimal residual disease status, conditioning, age, cytogenetic disease risk, type of consolidation chemotherapy, pre-HCT karyotype, and pre-HCT peripheral blood count recovery), the hazard ratios for 2 or >2 induction courses versus 1 induction were 1.16 (95% CI, .73 to 1.85, P = .53) and 2.63 (95% CI, 1.24 to 5.57, P = .011) for overall mortality, and 2.10 (95% CI, 1.27 to 3.48, P = .004) and 3.32 (95% CI, 1.42 to 7.78, P = .006), respectively, for relapse. These findings indicate that the number of induction courses required to achieve morphological remission in AML adds prognostic information for post-HCT outcome that is independent of other prognostic factors.

Hematopoietic stem-cell transplantation for advanced systemic mastocytosis

PURPOSE

Advanced systemic mastocytosis (SM), a fatal hematopoietic malignancy characterized by drug resistance, has no standard therapy. The effectiveness of allogeneic hematopoietic stem-cell transplantation (alloHCT) in SM remains unknown.

PATIENTS AND METHODS

In a global effort to define the value of HCT in SM, 57 patients with the following subtypes of SM were evaluated: SM associated with clonal hematologic non-mast cell disorders (SM-AHNMD; n = 38), mast cell leukemia (MCL; n = 12), and aggressive SM (ASM; n = 7). Median age of patients was 46 years (range, 11 to 67 years). Donors were HLA-identical (n = 34), unrelated (n = 17), umbilical cord blood (n = 2), HLA-haploidentical (n = 1), or unknown (n = 3). Thirty-six patients received myeloablative conditioning (MAC), and 21 patients received reduced-intensity conditioning (RIC).

RESULTS

Responses in SM were observed in 40 patients (70%), with complete remission in 16 patients (28%). Twelve patients (21%) had stable disease, and five patients (9%) had primary refractory disease. Overall survival (OS) at 3 years was 57% for all patients, 74% for patients with SM-AHNMD, 43% for those with ASM, and 17% for those with MCL. The strongest risk factor for poor OS was MCL. Survival was also lower in patients receiving RIC compared with MAC and in patients having progression compared with patients having stable disease or response.

CONCLUSION

AlloHCT was associated with long-term survival in patients with advanced SM. Although alloHCT may be considered as a viable and potentially curative therapeutic option for advanced SM in the meantime, given that this is a retrospective analysis with no control group, the definitive role of alloHCT will need to be determined by a prospective trial.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for "prime time"?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a "one size fits all" approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Comparison of chimerism and minimal residual disease monitoring for relapse prediction after allogeneic stem cell transplantation for adult acute lymphoblastic leukemia

Little data are available on the relative merits of chimerism and minimal residual disease (MRD) monitoring for relapse prediction after allogeneic hematopoietic stem cell transplantation (HCT). We performed a retrospective analysis of serial chimerism assessments in 101 adult HCT recipients with acute lymphoblastic leukemia (ALL) and of serial MRD assessments in a subgroup of 22 patients. All patients had received myeloablative conditioning. The cumulative incidence of relapse was significantly higher in the patients with increasing mixed chimerism (in-MC) compared with those with complete chimerism, low-level MC, and decreasing MC, but the sensitivity of in-MC detection with regard to relapse prediction was only modest. In contrast, MRD assessment was highly sensitive and specific. Patients with MRD positivity after HCT had the highest incidence of relapse among all prognostic groups analyzed. The median time from MRD positivity to relapse was longer than the median time from detection of in-MC, but in some cases in-MC preceded MRD positivity. We conclude that MRD assessment is a powerful prognostic tool that should be included in the routine post-transplantation monitoring of patients with ALL, but chimerism analysis may provide additional information in some cases. Integration of these tools and clinical judgment should allow optimal decision making with regard to post-transplantation therapeutic interventions.

Comparison of minimal residual disease as outcome predictor for AML patients in first complete remission undergoing myeloablative or nonmyeloablative allogeneic hematopoietic cell transplantation

Minimal residual disease (MRD) is associated with adverse outcome in AML after myeloablative (MA) hematopoietic cell transplantation (HCT). We compared this association with that seen after nonmyeloablative (NMA) conditioning in 241 adults receiving NMA (n=86) or MA (n=155) HCT for AML in first remission with pre-HCT bone marrow aspirates assessed by flow cytometry. NMA patients were older and had more comorbidities and secondary leukemias. Three-year relapse estimates were 28% and 57% for MRD^neg and MRD^pos NMA patients, and 22% and 63% for MA patients. Three-year overall survival (OS) estimates were 48% and 41% for MRD^neg and MRD^pos NMA patients and 76% and 25% for MA patients. This similar OS after NMA conditioning was largely accounted for by higher non-relapse mortality (NRM) in MRD^neg (30%) compared to MRD^pos (10%) patients, whereas the reverse was found for MRD^neg (7%) and MRD^pos (23%) MA patients. A statistically significant difference between MA and NMA patients in the association of MRD with OS (P<0.001) and NRM (P=0.002) but not relapse (P=0.17) was confirmed. After adjustment, the risk of relapse was 4.51-times (P<0.001) higher for MRD^pos patients. These data indicate that the negative impact of MRD on relapse risk is similar after NMA and MA conditioning.

Relapse assessment following allogeneic SCT in patients with MDS and AML

Options to pre-emptively treat impending relapse of myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML) after allogeneic haematopoietic stem cell transplantation (allo-SCT) continuously increase. In recent years, the spectrum of diagnostic methods and parameters to perform post-transplant monitoring in patients with AML and MDS has grown. Cytomorphology, histomorphology, and chimaerism analysis are the mainstay in any panel of post-transplant monitoring. This may be individually combined with multiparameter flow cytometry (MFC) for the detection of residual cells with a leukaemia phenotype and quantitative real-time polymerase chain reaction (RQ-PCR) to assess gene expression, e.g., of WT1 or the residual mutation load (e.g., in case of an NPM1 mutation). Data evaluating the aforementioned methods alone or in combination are discussed in this review with particular emphasis on data pointing towards their suitability to steer pre-emptive post-transplant interventions such as immunotherapy, chemotherapy or therapy with demethylating agents.

Effect of postremission therapy before reduced-intensity conditioning allogeneic transplantation for acute myeloid leukemia in first complete remission

The impact of pretransplant (hematopoietic cell transplantation [HCT]) cytarabine consolidation therapy on post-HCT outcomes has yet to be evaluated after reduced-intensity or nonmyeloablative conditioning. We analyzed 604 adults with acute myeloid leukemia in first complete remission (CR1) reported to the Center for International Blood and Marrow Transplant Research who received a reduced-intensity or nonmyeloablative conditioning HCT from an HLA-identical sibling, HLA-matched unrelated donor, or umbilical cord blood donor from 2000 to 2010. We compared transplant outcomes based on exposure to cytarabine postremission consolidation. Three-year survival rates were 36% (95% confidence interval [CI], 29% to 43%) in the no consolidation arm and 42% (95% CI, 37% to 47%) in the cytarabine consolidation arm (P = .16). Disease-free survival was 34% (95% CI, 27% to 41%) and 41% (95% CI, 35% to 46%; P = .15), respectively. Three-year cumulative incidences of relapse were 37% (95% CI, 30% to 44%) and 38% (95% CI, 33% to 43%), respectively (P = .80). Multivariate regression confirmed no effect of consolidation on relapse, disease-free survival, and survival. Before reduced-intensity or nonmyeloablative conditioning HCT, these data suggest pre-HCT consolidation cytarabine does not significantly alter outcomes and support prompt transition to transplant as soon as morphologic CR1 is attained. If HCT is delayed while identifying a donor, our data suggest that consolidation does not increase transplant treatment-related mortality and is reasonable if required.

Achieving stringent CR is essential before reduced-intensity conditioning allogeneic hematopoietic cell transplantation in AML

Reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (allo-HCT) can cure patients with AML in CR. However, relapse after RIC allo-HCT may indicate heterogeneity in the stringency of CR. Strict definition of CR requires no evidence of leukemia by both morphologic and flow cytometric criteria. We re-evaluated 85 AML patients receiving RIC allo-HCT in CR to test if a strict definition of CR had direct implications for the outcome. These patients had leukemia immunophenotype documented at diagnosis and analyzed at allo-HCT. Eight (9.4%) had persistent leukemia by flow cytometric criteria at allo-HCT. The patients with immunophenotypic persistent leukemia had a significantly increased relapse (hazard ratio (HR): 3.7; 95% confidence interval (CI): 1.3-10.3, P=0.01) and decreased survival (HR: 2.9; 95% CI: 1.3-6.4, P<0.01) versus 77 patients in CR by both morphology and flow cytometry. However, the pre-allo-HCT bone marrow (BM) blast count (that is, 0-4%) was not significantly associated with risks of relapse or survival. These data indicate the presence of leukemic cells, but not the BM blast count affects survival. A strict morphologic and clinical lab flow cytometric definition of CR predicts outcomes after RIC allo-HCT, and therefore is critical to achieve at transplantation.

Significance of minimal residual disease before myeloablative allogeneic hematopoietic cell transplantation for AML in first and second complete remission

Minimal residual disease (MRD) before myeloablative hematopoietic cell transplantation (HCT) is associated with adverse outcome in acute myeloid leukemia (AML) in first complete remission (CR1). To compare this association with that for patients in second complete remission (CR2) and to examine the quantitative impact of MRD, we studied 253 consecutive patients receiving myeloablative HCT for AML in CR1 (n = 183) or CR2 (n = 70) who had pre-HCT marrow aspirates analyzed by 10-color flow cytometry. Three-year estimates of overall survival were 73% (64%-79%) and 32% (17%-48%) for MRDneg and MRDpos CR1 patients, respectively, and 73% (57%-83%) and 44% (21%-65%) for MRDneg and MRDpos CR2 patients, respectively. Similar estimates of relapse were 21% (14%-28%) and 58% (41%-72%) for MRDneg and MRDpos CR1 patients, respectively, and 19% (9%-31%) and 68% (41%-85%) for MRDneg and MRDpos CR2 patients, respectively. Among the MRDpos patients, there was no statistically significant evidence that increasing levels of MRD were associated with increasing risks of relapse and death. After multivariable adjustment, risks of death and relapse were 2.61 times and 4.90 times higher for MRD(pos) patients (P < .001). Together, our findings indicate that the negative impact of pre-HCT MRD is similar for AML in CR1 and CR2 with even minute levels (≤ 0.1%) as being associated with adverse outcome.