Current Opinion in Hematology:
LYMPHOID BIOLOGY AND DISEASES: Edited by Nancy Berliner
Minimal residual disease monitoring in childhood acute lymphoblastic leukemia
Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
Correspondence to Dario Campana, MD, PhD, Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Centre for Translational Medicine,14 Medical Drive, Level 9 South, Singapore 117599, Singapore. Tel: +65 6601 2666; fax: +65 6779 7486; e-mail: email@example.com@stjude.org
Purpose of review: This review summarizes recent advances in the application of minimal residual disease (MRD) testing in childhood acute lymphoblastic leukemia (ALL).
Recent findings: Polymerase chain reaction amplification of antigen receptor genes, one of the two main methods to study MRD in ALL, could be made more rapid, sensitive and informative by the application of next-generation sequencing technologies. Advances in flow cytometric detection of MRD, the other main method, include the identification of new immunophenotypic markers to recognize ALL cells, the development of computerized approaches to automate data analysis, and the generation of instruments that can rapidly screen large number of cells for immunophenotypic abnormalities while visualizing their morphology. Recent data further corroborate the prognostic value of MRD at early time points during therapy, demonstrate the prognostic significance of MRD among ALL subtypes, and indicate that presenting features can complement the prognostic utility of MRD.
Summary: MRD is replacing morphology to measure treatment response in ALL and is being used, with promising results, for risk-stratification in clinical protocols. Recent studies provide further evidence of its prognostic significance and point to possible strategies to increase the reliability, applicability and sensitivity of MRD testing.
In patients with leukemia, minimal residual disease (MRD) signifies leukemic cells undetectable by morphologic examination of bone marrow smears. Acute lymphoblastic leukemia (ALL) has been at the forefront of the development of MRD methods . Progress in introducing MRD testing into the clinic was not initially widely supported as some investigators were concerned that the distribution of leukemic cells during treatment might be too heterogeneous for MRD testing to be accurate. In fact, the strong correlation between levels of MRD and relapse risk suggests that, at least at the early stages of therapy, ALL distribution is quite homogeneous . Other investigators insisted that progress in ALL prognostication could only occur by focusing on the genetics of leukemic cells. However, MRD measurements should be inherently more informative than any leukemic cell features as they reflect the effect of several other variables that influence treatment response and outcome, including variations in drug dosage, pharmacogenomics and pharmacodynamics factors, the effect of the microenvironment, and patient compliance . Ultimately, confidence in the clinical utility of MRD has grown with improvements in methodology and the strength of many correlative studies, and MRD testing is gradually superceding morphology as the best means to assess treatment response and define ‘remission’ in patients with ALL. This article provides an update on recent advances in the application of MRD studies to childhood ALL.
RECENT DEVELOPMENTS IN MINIMAL RESIDUAL DISEASE TECHNOLOGY
Two main approaches have been demonstrated to provide clinically meaningful MRD results: PCR amplification of immunoglobulin and T-cell receptor (TCR) genes, and flow cytometric detection of aberrant immunophenotypes [2,3]. PCR amplification of oncogenic fusion transcripts can only be applied to a subset of patients, that is, those with the most prevalent gene fusions, and suffers from lack of quantitative power [4▪]; hence, it is used less frequently.
Clonal rearrangements of immunoglobulin and TCR genes occur in approximately 90% of patients with ALL. By targeting these genes, after identifying them at diagnosis, MRD monitoring with a sensitivity of one leukemic cell in 100 000 normal bone marrow cells (or 0.001%) can be attained [2,4▪,5]. Because of the extensive efforts of the investigators participating in the BIOMED-2 Concerted Action BMH4-CT98–3936 project, the methods have been extensively optimized and standardized, thus facilitating their implementation in other laboratories [2,4▪]. This approach, however, requires sequencing of diagnostic DNA, identification of suitable rearrangements (often more than one), synthesis of corresponding primers and development of PCR conditions that are optimal for each rearrangement . This process is time consuming and usually precludes analysis of MRD at early time points (e.g., day 15) in a timely fashion. The advent of massive parallel sequencing technologies, and their decreasing cost, has opened the possibility of using consensus primers (a set of primers that can be used to amplify all possible rearranged immunoglobulin or TCR segments) and parallel sequencing to identify the most prevalent rearrangement at diagnosis . These rearrangements are then searched among those amplified in the same way in the follow-up samples, obviating the need to develop reagents and PCR conditions for each patient. The specificity and sensitivity of this approach is potentially very high and, if sufficient DNA is available for study, it can reach 1 in 106 and beyond . In initial tests of this method applied to ALL, Faham et al. studied diagnostic and follow-up samples from 10 patients using a comprehensive set of consensus primers: they could identify all five samples that were MRD-positive according to established flow cytometry and PCR methods, with highly concordant estimates of MRD levels between the established and the new method. Interestingly, one of the five samples that were MRD-negative by both flow cytometry and conventional PCR had unambiguous leukemia-derived sequences in the range of one in a million. This approach holds potential for greatly facilitating molecular MRD studies in ALL and it may well supplant the current method.
Leukemia-associated immunophenotypes that can be monitored by flow cytometry are expressed by leukemic lymphoblasts in the majority of patients and allow MRD detection with a sensitivity of 0.01%. However, identifying the immunophenotypic difference between ALL and normal cells takes much training and experience. The greater the difference between the overall immunophenotypic profiles of leukemic and normal cells, the easier it is to recognize ALL cells. On the basis of this principle, we sought to identify additional markers that would make ALL cells more distinct. This task traditionally relied on a heuristic approach, largely based on trial and error [8–10]. Encouraged by the promising results of a pilot study that identified CD58 as a useful marker for MRD studies , we compared genome-wide gene expression of lymphoblasts from 270 patients with newly diagnosed childhood ALL to that of sorted normal CD19+CD10+ B-cell progenitors from four healthy donors, that is, cells with immunophenotypic features similar to those of leukemic lymphoblasts [12▪]. Among genes differentially expressed by genome-wide expression array analysis, we selected a group of 30 for further studies based on their highly abnormal expression at the mRNA level in a substantial proportion of ALL cases and on the availability of specific antibodies suitable for routine flow cytometric studies [12▪]. We then tested their expression by flow cytometry in 200 B-lineage ALL and 61 nonleukemic bone marrow samples, including in the analysis recovering bone marrow samples, which are particularly challenging in MRD studies of ALL because of their high proportion of normal immature lymphoid cells. Of the 30 markers, 22 were differentially expressed in up to 81% of ALL cases [12▪], including markers also found by other investigators to be differentially expressed in ALL such as CD304  and CD123 . The reliability of the new markers was further corroborated by comparisons using paired diagnosis–relapse samples, which demonstrated that their expression remained stable during leukemia progression [12▪]. The addition of these new markers considerably improved existing MRD panels by allowing reliable MRD monitoring by flow cytometry in all patients with a potential sensitivity of one in 100 000 [12▪]. Other markers recently reported to hold potential for MRD studies include CD81 , CD49f , and CD11b , the latter also having been found to be overexpressed in a substantial number ALL cases in our gene expression array comparison [12▪].
Attempts to automate the interpretation of flow cytometric MRD data are now being made . Fiser et al. developed a method based on hierarchical clustering analysis which yielded MRD results that correlated well with standard procedures. These new approaches, if incorporated into easily accessible software, should be a useful aid and may ultimately automate the interpretation process entirely. These efforts should take into account the fact that the intensity of marker expression may change during chemotherapy . Dworzak et al. recently reported a study of some of the markers in patients who were MRD positive through sequential testing. They found that downregulation of CD10 and CD34 expression observed early during chemotherapy reverted to the levels recorded at diagnosis after glucocorticoids were stopped. Glucocorticoids were also linked to upregulation of CD20 and changes in CD45 expression, whereas changes in CD11b expression occurred later .
A recent study tested the potential of an entirely different approach to immunophenotypic analysis of MRD, based on high-speed cell imaging scanning technology . This method has the potential to identify immunophenotypically aberrant cells among 1 million or more normal cells and then determine their morphology to ensure that the signals detected are not artifacts but originate from viable lymphoblasts .
Because current MRD tests are complex and require specific expertise, they should be performed in specialized laboratories. PCR studies are typically performed in reference laboratories but flow cytometric studies, which require instruments and reagents widely available for leukemia immunophenotyping, are often attempted by investigators without the necessary specialized skills, which may lead to erroneous results. Recognizing the potentially disastrous consequences of this, cooperative groups generally submit samples to reference laboratories with demonstrated expertise [22–24], or share the workload among a larger number of laboratories after extensive cross-testing and standardization efforts [25–27].
CORRELATIVE STUDIES WITH TREATMENT OUTCOME
The prognostic significance of MRD in childhood ALL is unquestionable and has been demonstrated in numerous correlative studies using either PCR or flow cytometry, measuring MRD at various intervals during therapy, in the context of different chemotherapy regimens, and including children with first-relapse ALL who achieve a second remission [5,22,23,28–36,37▪,38–44]. In addition to predicting outcome in the context of chemotherapy, MRD also provides valuable information when measured prior to and after allogeneic hematopoietic stem cell transplant (HSCT) [45–48].
A large study by Conter et al.[37▪] illustrates the prognostic importance of MRD. These authors used PCR to obtain MRD measurements on days 33 and 78 in 3184 patients with newly diagnosed B-lineage ALL enrolled in the Associazione Italiana Ematologia Oncologia Pediatrica – Berlin Frankfurt Münster (AIEOP-BFM) ALL 2000 protocol, and identified three risk-categories based on MRD levels. Patients with MRD less than 0.01% on days 33 and 78 (42%) had a 5-year event-free survival (EFS) of 92.3%, those with MRD at least 0.1% on day 78 (6%) had an EFS of 50.1% and the remaining patients (52%) had an EFS of 77.6% (1.3). MRD was a better predictor of outcome than leukocyte count, age, early response to prednisone and genetic subtype. Importantly, MRD was predictive of outcome even among subsets of patients defined by TEL-AML1, high hyperdiploidy, or BCR-ABL1. In a recently reported study, Schrappe et al.[49▪] used similar methodology to measure MRD in 464 patients with T-ALL. Using the same cut-off levels applied by Conter et al. in the B-lineage ALL cohort, they found that only 16% were MRD less than 0.01% on days 33 and 78, 21% had MRD at least 0.1% on day 78 and 63% had intermediate MRD levels. MRD less than 0.01% at the end of induction was the best indicator of a favorable prognosis, whereas patients with MRD at least 0.1% on day 78 had a high risk of relapse. Notably, patients converting to MRD negativity on day 78 (32%) had a favorable outcome. Among 99 infants with ALL enrolled in the Interfant-99 protocol, Van der Velden et al. found that all those with MRD at least 0.01% at the end of induction and/or consolidation (26%) relapsed, whereas relapse occurred in only 13% of those with MRD less than 0.01% at both time points (44%); the remaining patients had a relapse rate of 31%. Finally, Bowman et al.[51▪] recently reported that MRD measured in peripheral blood on day 8 and in the bone marrow on day 29 were strong prognostic factors in children with B-lineage ALL and high-risk presenting clinical features who received augmented therapy.
Studies performed during remission induction therapy are emerging as being particularly informative. Sutton et al. used PCR to measure MRD at various time points during treatment in 108 patients enrolled on the Australian and New Zealand Children's Cancer Study Group Study VII and found that day 15 was the best early MRD time point to predict risk of relapse. Basso et al. used flow cytometry to examine bone marrow samples from 830 children with ALL collected on day 15 of treatment, after 14 days of steroids and one dose of vincristine, daunorubicin, and asparaginase, as well as intrathecal methotrexate. One group of patients, representing 42% of the cohort, had less than 0.1% ALL cells, and had a 5-year cumulative incidence of relapse of 7.5%. A second group (47%) had MRD of 0.1% to less than 10% and a relapse rate of 17.5%. Finally, 11% of patients had high MRD of 10% or more and a relapse rate of 47.2%. In a multivariate analysis, MRD was the strongest prognostic factor among those available by day 15; even when MRD detected by PCR at later time points was added to the model, MRD on day 15 retained prognostic significance.
The informative potential of MRD measured at early time points has practical implications because these can be performed with a simplified, low-cost, flow cytometry assay. To this end, we found that bone marrow normal lymphoid progenitors (CD19+, CD10+, and/or CD34+) are exquisitely sensitive to corticosteroids and other antileukemic drugs . In patients with B-lineage ALL, cells with this phenotype detected early in treatment indicate residual disease. MRD detection by this simplified assay correlated well with those of more complex flow cytometric and molecular MRD tests . On the basis of these results, we have initiated treatment protocols relying on the simplified test to identify good early responders who are offered less intensive chemotherapy (R. Ribeiro, G. Rivera, D. Campana, E. Coustan-Smith, F. Pedrosa, I. Sidhom, K. Shaaban, et al., unpublished results). Other investigators have also recently confirmed the informative value of this approach . Such studies represent a good starting point for laboratories interested in implementing MRD studies and are particularly well suited for centers with limited resources, because they require only a very small antibody panel and basic instrumentation.
MRD testing has changed the definition of remission in ALL and set a new standard by which the efficacy of antileukemia therapy can be measured. MRD levels are now used for risk-assignment in several treatment protocols for childhood ALL. In the now closed St Jude Total XV study for children and adolescents with ALL, MRD was measured on days 19 and 46 of treatment and chemotherapy, and the data were used to determine a final risk classification , resulting in outstanding overall cure rates. Regardless, in this study, high MRD levels (≥1%) at the end of induction (a criterion for HSCT in first remission) remained an adverse predictor of outcome and the only independent prognostic factor (in addition to CNS3 status at diagnosis or traumatic lumbar puncture). Lankester et al.  stratified 48 children with ALL undergoing HSCT according to the MRD levels before transplant. Those with MRD at least 0.01% (n = 18) were eligible for early tapering of cyclosporine post-HSCT and donor lymphocyte infusions. Relapses appeared to occur later and several presented at extramedullary sites, suggesting some modulatory effect from the intervention . Although event-free survival in this study (19%) was ultimately not better than that of previous trials, further attempts are warranted to reduce the relapse rate post-HSCT for patients with MRD prior to transplant, and/or strive for a further reduction of MRD before beginning the transplant conditioning regimen .
The relative weight of different prognostic factors in ALL changes as therapy improves and new prognostically significant subsets, such as B-lineage ALL with abnormalities of the IKZF1 gene  or early T-cell precursor , must now be taken into account. Although MRD measurements will most likely remain central to the modern treatment of ALL, their predictive power might be improved by integrating it with that of other factors. To this end, Rabin et al. found that absolute lymphocyte counts on day 29 could improve MRD-based predictions in children treated in the Children's Oncology Group P9900 protocols. Lonnerholm et al. reported data suggesting that results of vincristine and doxorubicin resistance determined in vitro might add to MRD measurements on day 29. Finally, Waanders et al. integrated MRD and IKZF1 gene status to predict 79% of the relapses (with 93% specificity) occurring in a group of 131 B-lineage ALL patients.
In sum, MRD studies have revolutionized risk-stratification in childhood ALL and have multiple applications in the management of patients. MRD is also beginning to be used to determine the efficacy of new anti-ALL agents [60▪], and should be a valuable tool to accelerate the discovery of agents with the highest antileukemic effect.
Conflicts of interest
There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
▪ of special interest
▪▪ of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (pp. 341–342).
1. Campana D. Minimal residual disease in acute lymphoblastic leukemia. Hematol Am Soc Hematol Educ Program 2010; 2010:7–12.
2. van der Velden VH, van Dongen JJ. MRD detection in acute lymphoblastic leukemia patients using Ig/TCR gene rearrangements as targets for real-time quantitative PCR. Methods Mol Biol 2009; 538:115–150.
3. Coustan-Smith E, Campana D. Immunologic minimal residual disease detection in acute lymphoblastic leukemia: a comparative approach to molecular testing. Best Pract Res Clin Haematol 2010; 23:347–358.
4▪. Bruggemann M, Schrauder A, Raff T, et al. Standardized MRD quantification in European ALL trials: proceedings of the Second International Symposium on MRD assessment in Kiel, Germany, 18–20 September 2008. Leukemia 2010; 24:521–535.
A comprehensive summary of MRD trials in Europe.
5. Stow P, Key L, Chen X, et al. Clinical significance of low levels of minimal residual disease at the end of remission induction therapy in childhood acute lymphoblastic leukemia. Blood 2010; 115:4657–4663.
6. Boyd SD, Marshall EL, Merker JD, et al. Measurement and clinical monitoring of human lymphocyte clonality by massively parallel VDJ pyrosequencing. Sci Transl Med 2009; 1:12ra23.
7. Faham M, Willis T, Moorhead M, et al. Highly sensitive detection of minimal residual disease in acute lymphoblastic leukemia using next-generation sequencing of immunoglobulin heavy chain variable region. Blood 2011; 118:1089–1090.
8. Campana D, Coustan-Smith E. Detection of minimal residual disease in acute leukemia by flow cytometry. Cytometry 1999; 38:139–152.
9. Lucio P, Gaipa G, van Lochem EG, et al. BIOMED-I concerted action report: flow cytometric immunophenotyping of precursor B-ALL with standardized triple-stainings. BIOMED-1 Concerted Action Investigation of Minimal Residual Disease in Acute Leukemia: International Standardization and Clinical Evaluation. Leukemia 2001; 15:1185–1192.
10. DiGiuseppe JA, Fuller SG, Borowitz MJ. Overexpression of CD49f in precursor B-cell acute lymphoblastic leukemia: potential usefulness in minimal residual disease detection. Cytometry B Clin Cytom 2009; 76:150–155.
11. Chen JS, Coustan-Smith E, Suzuki T, et al. Identification of novel markers for monitoring minimal residual disease in acute lymphoblastic leukemia. Blood 2001; 97:2115–2120.
12▪. Coustan-Smith E, Song G, Clark C, et al. New markers for minimal residual disease detection in acute lymphoblastic leukemia. Blood 2011; 117:6267–6276.
This study identified several new markers for MRD monitoring by flow cytometry.
13. Solly F, Angelot F, Garand R, et al. CD304 is preferentially expressed on a subset of B-lineage acute lymphoblastic leukemia and represents a novel marker for minimal residual disease detection by flow cytometry. Cytometry A 2012; 81:17–24.
14. Djokic M, Bjorklund E, Blennow E, et al. Overexpression of CD123 correlates with the hyperdiploid genotype in acute lymphoblastic leukemia. Haematologica 2009; 94:1016–1019.
15. Muzzafar T, Medeiros LJ, Wang SA, et al. Aberrant underexpression of CD81 in precursor B-cell acute lymphoblastic leukemia: utility in detection of minimal residual disease by flow cytometry. Am J Clin Pathol 2009; 132:692–698.
16. Rhein P, Mitlohner R, Basso G, et al. CD11b is a therapy resistance and minimal residual disease-specific marker in precursor B-cell acute lymphoblastic leukemia. Blood 2010; 115:3763–3771.
17. Pedreira CE, Costa ES, Almeida J, et al. A probabilistic approach for the evaluation of minimal residual disease by multiparameter flow cytometry in leukemic B-cell chronic lymphoproliferative disorders. Cytometry A 2008; 73A:1141–1150.
18. Fiser K, Sieger T, Schumich A, et al. Detection and monitoring of normal and leukemic cell populations with hierarchical clustering of flow cytometry data. Cytometry A 2012; 81:25–34.
19. Gaipa G, Basso G, Maglia O, et al. Drug-induced immunophenotypic modulation in childhood ALL: implications for minimal residual disease detection. Leukemia 2005; 19:49–56.
20. Dworzak MN, Gaipa G, Schumich A, et al. Modulation of antigen expression in B-cell precursor acute lymphoblastic leukemia during induction therapy is partly transient: Evidence for a drug-induced regulatory phenomenon. Results of the AIEOP-BFM-ALL-FLOW-MRD-Study Group. Cytometry B Clin Cytom 2010; 78:147–153.
21. Liu X, Hsieh HB, Campana D, Bruce RH. A new method for high speed, sensitive detection of minimal residual disease. Cytometry A 2012; 81:169–175.
22. Borowitz MJ, Devidas M, Hunger SP, et al. Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia and its relationship to other prognostic factors. a Children's Oncology Group study. Blood 2008; 111:5477–5485.
23. Basso G, Veltroni M, Valsecchi MG, et al. Risk of relapse of childhood acute lymphoblastic leukemia is predicted by flow cytometric measurement of residual disease on day 15 bone marrow. J Clin Oncol 2009; 27:5168–5174.
24. Pui CH, Campana D, Pei D, et al. Treating childhood acute lymphoblastic leukemia without cranial irradiation. N Engl J Med 2009; 360:2730–2741.
25. Irving J, Jesson J, Virgo P, et al. Establishment and validation of a standard protocol for the detection of minimal residual disease in B lineage childhood acute lymphoblastic leukemia by flow cytometry in a multicenter setting. Haematologica 2009; 94:870–874.
26. Luria D, Rosenthal E, Steinberg D, et al. Prospective comparison of two flow cytometry methodologies for monitoring minimal residual disease in a multicenter treatment protocol of childhood acute lymphoblastic leukemia. Cytometry B Clin Cytom 2010; 78:365–371.
27. Mejstrikova E, Fronkova E, Kalina T, et al. Detection of residual B precursor lymphoblastic leukemia by uniform gating flow cytometry. Pediatr Blood Cancer 2010; 54:62–70.
28. Brisco MJ, Condon J, Hughes E, et al. Outcome prediction in childhood acute lymphoblastic leukaemia by molecular quantification of residual disease at the end of induction. Lancet 1994; 343:196–200.
29. Cave H, van der Werff ten Bosch J, Suciu S, et al. Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia. European Organization for Research and Treatment of Cancer: Childhood Leukemia Cooperative Group. N Engl J Med 1998; 339:591–598.
30. Coustan-Smith E, Behm FG, Sanchez J, et al. Immunological detection of minimal residual disease in children with acute lymphoblastic leukaemia. Lancet 1998; 351:550–554.
31. van Dongen JJ, Seriu T, Panzer-Grumayer ER, et al. Prognostic value of minimal residual disease in acute lymphoblastic leukaemia in childhood. Lancet 1998; 352:1731–1738.
32. Coustan-Smith E, Sancho J, Hancock ML, et al. Clinical importance of minimal residual disease in childhood acute lymphoblastic leukemia. Blood 2000; 96:2691–2696.
33. Coustan-Smith E, Sancho J, Behm FG, et al. Prognostic importance of measuring early clearance of leukemic cells by flow cytometry in childhood acute lymphoblastic leukemia. Blood 2002; 100:52–58.
34. Dworzak MN, Froschl G, Printz D, et al. Prognostic significance and modalities of flow cytometric minimal residual disease detection in childhood acute lymphoblastic leukemia. Blood 2002; 99:1952–1958.
35. Zhou J, Goldwasser MA, Li A, et al. Quantitative analysis of minimal residual disease predicts relapse in children with B-lineage acute lymphoblastic leukemia in DFCI ALL Consortium Protocol 95-01. Blood 2007; 110:1607–1611.
36. Sutton R, Venn NC, Tolisano J, et al. Clinical significance of minimal residual disease at day 15 and at the end of therapy in childhood acute lymphoblastic leukaemia. Br J Haematol 2009; 146:292–299.
37▪. Conter V, Bartram CR, Valsecchi MG, et al. Molecular response to treatment redefines all prognostic factors in children and adolescents with B-cell precursor acute lymphoblastic leukemia: results in 3184 patients of the AIEOP-BFM ALL 2000 study. Blood 2010; 115:3206–3214.
This study demonstrated the prognostic significance of MRD in B-lineage ALL regardless of presenting features in a large cohort of patients.
38. Yamaji K, Okamoto T, Yokota S, et al. Minimal residual disease-based augmented therapy in childhood acute lymphoblastic leukemia: a report from the Japanese Childhood Cancer and Leukemia Study Group. Pediatr Blood Cancer 2010; 55:1287–1295.
39. Katsibardi K, Moschovi MA, Braoudaki M, et al. Sequential monitoring of minimal residual disease in acute lymphoblastic leukemia: 7-year experience in a pediatric hematology/oncology unit. Leuk Lymphoma 2010; 51:846–852.
40. Meleshko AN, Savva NN, Fedasenka UU, et al. Prognostic value of MRD-dynamics in childhood acute lymphoblastic leukemia treated according to the MB-2002/2008 protocols. Leuk Res 2011; 35:1312–1320.
41. Eckert C, Biondi A, Seeger K, et al. Prognostic value of minimal residual disease in relapsed childhood acute lymphoblastic leukaemia. Lancet 2001; 358:1239–1241.
42. Coustan-Smith E, Gajjar A, Hijiha N, et al. Clinical significance of minimal residual disease in childhood acute lymphoblastic leukemia after first relapse. Leukemia 2004; 18:499–504.
43. Paganin M, Zecca M, Fabbri G, et al. Minimal residual disease is an important predictive factor of outcome in children with relapsed ‘high-risk’ acute lymphoblastic leukemia. Leukemia 2008; 22:2193–2200.
44. Raetz EA, Borowitz MJ, Devidas M, et al. Reinduction platform for children with first marrow relapse in acute lymphoblastic lymphoma. J Clin Oncol 2008; 26:3971–3978.
45. Krejci O, van der Velden V, Bader P, et al. Level of minimal residual disease prior to haematopoietic stem cell transplantation predicts prognosis in paediatric patients with acute lymphoblastic leukaemia: a report of the Pre-BMT MRD Study Group. Bone Marrow Transplant 2003; 32:849–851.
46. Bader P, Kreyenberg H, Henze GH, et al. Prognostic value of minimal residual disease quantification before allogeneic stem-cell transplantation in relapsed childhood acute lymphoblastic leukemia: the ALL-REZ BFM Study Group. J Clin Oncol 2009; 27:377–384.
47. Leung W, Campana D, Yang J, et al. High success rate of hematopoietic cell transplantation regardless of donor source in children with very high-risk leukemia. Blood 2011; 118:223–230.
48. Zhao XS, Liu YR, Zhu HH, et al. Monitoring MRD with flow cytometry: an effective method to predict relapse for ALL patients after allogeneic hematopoietic stem cell transplantation. Ann Hematol 2012; 91:183–192.
49▪. Schrappe M, Valsecchi MG, Bartram CR, et al. Late MRD response determines relapse risk overall and in subsets of childhood T-cell ALL: results of the AIEOP-BFM-ALL 2000 study. Blood 2011; 118:2077–2084.
This study demonstrated the prognostic significance of MRD in T-lineage ALL.
50. van der Velden V, Corral L, Valsecchi MG, et al. Prognostic significance of minimal residual disease in infants with acute lymphoblastic leukemia treated within the Interfant-99 protocol. Leukemia 2009; 23:1073–1079.
51▪. Bowman WP, Larsen EL, Devidas M, et al. Augmented therapy improves outcome for pediatric high risk acute lymphocytic leukemia: results of Children's Oncology Group trial P9906. Pediatr Blood Cancer 2011; 57:569–577.
This study demonstrated the clinical significance of MRD in patients with high-risk ALL treated with augmented therapy.
52. Coustan-Smith E, Ribeiro RC, Stow P, et al. A simplified flow cytometric assay identifies children with acute lymphoblastic leukemia who have a superior clinical outcome. Blood 2006; 108:97–102.
53. Koh KN, Park M, Kim BE, et al. Prognostic significance of minimal residual disease detected by a simplified flow cytometric assay during remission induction chemotherapy in children with acute lymphoblastic leukemia. Korean J Pediatr 2010; 53:957–964.
54. Lankester AC, Bierings MB, Van Wering ER, et al. Preemptive alloimmune intervention in high-risk pediatric acute lymphoblastic leukemia patients guided by minimal residual disease level before stem cell transplantation. Leukemia 2010; 24:1462–1469.
55. Mullighan CG, Su X, Zhang J, et al. Deletion of IKZF1 and prognosis in acute lymphoblastic leukemia. N Engl J Med 2009; 360:470–480.
56. Coustan-Smith E, Mullighan CG, Onciu M, et al. Early T-cell precursor leukaemia: a subtype of very high-risk acute lymphoblastic leukaemia. Lancet Oncol 2009; 10:147–156.
57. Rabin KR, Gramatges MM, Borowitz MJ, et al
. Absolute lymphocyte counts refine minimal residual disease-based risk stratification in childhood acute lymphoblastic leukemia. Pediatr Blood Cancer 2011. doi:10.1002/pbc.23395. [Epub ahead of print]
58. Lonnerholm G, Thorn I, Sundstrom C, et al. In vitro cellular drug resistance adds prognostic information to other known risk-factors in childhood acute lymphoblastic leukemia. Leuk Res 2011; 35:472–478.
59. Waanders E, van der Velden VH, van der Schoot CE, et al. Integrated use of minimal residual disease classification and IKZF1 alteration status accurately predicts 79% of relapses in pediatric acute lymphoblastic leukemia. Leukemia 2011; 25:254–258.
60▪. Topp MS, Kufer P, Gokbuget N, et al. Targeted therapy with the T-cell-engaging antibody blinatumomab of chemotherapy-refractory minimal residual disease in B-lineage acute lymphoblastic leukemia patients results in high response rate and prolonged leukemia-free survival. J Clin Oncol 2011; 29:2493–2498.
An excellent example of using MRD as an eligibility criteria for a trial with a novel agent.
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