Monitoring minimal residual disease in patients with MLL-AF6 fusion transcript-positive acute myeloid leukemia following allogeneic bone marrow transplantation

Use of Minimal Residual Disease in Acute Myeloid Leukemia Therapy

OPINION STATEMENT

The expanding availability of minimal or more precisely measurable residual disease (MRD) assessment in acute myeloid leukemia (AML) with its possible implications for therapeutic decisions is of high interest to clinicians treating AML patients. A variety of mostly retrospective studies have shown that AML patients with a positive MRD test, assessed by different techniques at defined cutoffs and time-points, are at significantly higher risk of relapse and experience shorter overall survival compared to MRD-negative patients. How this valuable information may be adapted in the daily routine of patients' treatment to distinguish individuals who need more aggressive therapy from the ones who can be spared additional therapy to avoid treatment-related toxicities is still being investigated. With the exception of MRD analyses in acute promyelocitic leukemia (APL), the clinical implications of MRD tests for the individual AML patient are still mostly unknown. We currently lack hard evidence that MRD-based therapy modulation during treatment or pre-emptive intervention in MRD-positive patients after therapy would improve outcomes in non-APL AML patients. These questions will be evaluated in prospective randomized clinical trials. Today, however, some conclusions with regard to MRD assessment in AML can be drawn from the published data and are reviewed in this article.

Clinical Challenges and Consequences of Measurable Residual Disease in Non-APL Acute Myeloid Leukemia

The ability to detect residual levels of leukemic blasts (measurable residual disease, MRD) has already been integrated in the daily routine for treatment of patients with chronic myeloid and acute lymphoblastic leukemia. In acute myeloid leukemia (AML), a variety of mostly retrospective studies have shown that individuals in AML remission who tested positive for MRD at specific time-points or had increasing MRD levels are at significantly higher risk of relapse and death compared to MRD-negative patients. However, these studies differ with respect to the "MRD-target", time-point of MRD determination, material analyzed, and method applied. How this probably very valuable MRD information in individual patients may be adapted in the daily clinical routine, e.g., to separate patients who need more aggressive therapies from those who may be spared additional-potentially toxic-therapies is still a work-in-progress. With the exception of MRD assessment in acute promyelocytic leukemia (APL), the lack of randomized, prospective trials renders MRD-based decisions and clinical implications in AML a difficult task. As of today, we still do not have proof that early intervention in MRD-positive AML patients would improve outcomes, although this is very likely. In this article, we review the current knowledge on non-APL AML MRD assessment and possible clinical consequences.

Enhancing acute myeloid leukemia therapy - monitoring response using residual disease testing as a guide to therapeutic decision-making

INTRODUCTION

Current standards for monitoring the response of acute myeloid leukemia (AML) are based on morphologic assessments of the bone marrow and recovery of peripheral blood counts. A growing experience is being developed to enhance the detection of small amounts of AML, or minimal residual disease (MRD). Areas covered: Available techniques include multi-color flow cytometry (MFC) of leukemia associated immunophenotypes (LAIP), quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) for detecting fusion and mutated genes (RUNX1-RUNX1T1, CBFB-MYH11, and NPM1), overexpression of genes such as WT1, and next generation sequencing (NGS) for MRD. Expert commentary: While MRD monitoring is standard of care in some leukemia subsets such as acute promyelocytic leukemia, this approach for the broader AML population does not universally predict outcomes as some patients may experience relapse in the setting of undetectable leukemia while others show no obvious disease progression despite MRD positivity. However, there are instances where MRD can identify patients at increased risk for relapse that may change recommended therapy. Currently, prospective investigations to define clinically relevant MRD thresholds are ongoing. Risk-adapted trials are needed to best define the use of MRD in the follow up of AML patients after initial induction therapy.

Relapse kinetics in acute myeloid leukaemias with MLL translocations or partial tandem duplications within the MLL gene

Correct action upon re-emergence of minimal residual disease in acute myeloid leukaemia (AML) patients has not yet been established. The applicability of demethylating agents and use of allogeneic stem cell transplantation will be dependent on pre-relapse AML growth rates. We here delineate molecular growth kinetics of AML harbouring MLL partial tandem duplication (MLL-PTD; 37 cases) compared to those harbouring MLL translocations (43 cases). The kinetics of MLL-PTD relapses was both significantly slower than those of MLL translocation positive ones (median doubling time: MLL-PTD: 24 d, MLL-translocations: 12 d, P = 0·015, Wilcoxon rank sum test), and displayed greater variation depending on additional mutations. Thus, MLL-PTD+ cases with additional RUNX1 mutations or FLT3-internal tandem duplication relapsed significantly faster than cases without one of those two mutations (Wilcoxon rank sum test, P = 0·042). As rapid relapses occurred in all MLL subgroups, frequent sampling are necessary to obtain acceptable relapse detection rates and times from molecular relapse to haematological relapse (blood sampling every second month: MLL-PTD: 75%/50 d; MLL translocations: 85%/25 d). In conclusion, in this cohort relapse kinetics is heavily dependent on AML subtype as well as additional genetic aberrations, with possibly great consequences for the rational choice of pre-emptive therapies.

Adult de novo acute myeloid leukemia with t(6;11)(q27;q23)

BACKGROUND

Acute myeloid leukemia (AML) with t(6;11)(q27;q23) is a well established but rare entity, and few studies have reported the full clinical, hematologic, and outcome data of patients with this disease.

METHODS

To characterize the features of t(6;11) AML, the authors searched the Cancer and Leukemia Group B (CALGB) cytogenetic database comprising 2667 adults with newly diagnosed, de novo AML and identified 16 patients (0.6%) with t(6;11). A review of the literature identified 33 adults with de novo t(6;11) AML for whom survival data were available.

RESULTS

CALGB patients had a median age of 45 years (range, 22-65 years) and commonly presented with French-American-British (FAB) subtype M4 or M5 (81%). Gingival involvement at presentation was common (31%). All patients with gingival involvement had FAB M4. Compared with other patients with M4 AML in the CALGB database (n = 429), patients with M4 and t(6;11) (n = 7) had a higher frequency of gingival hypertrophy at presentation (71% vs. 17%, P = 0.003). Patients with t(6;11) were more likely to be African American (P = 0.02) and to die during induction (P = 0.03) than those without t(6;11). The complete response (CR) rate was 69% (11 of 16 patients), and CR duration was short (median, 9 months). The estimated probability of 2-year survival was 13%. Both long-term survivors received allogeneic stem cell transplantation. The estimated probability of 2-year survival of patients reported in the literature was 15%.

CONCLUSIONS

Although the patient sample was small, the authors suggested that investigational approaches, including allogeneic transplantation, be considered for adults with t(6;11) AML.

Pediatric acute lymphoblastic leukemia

The outcome for children with acute lymphoblastic leukemia (ALL) has improved dramatically with current therapy resulting in an event free survival exceeding 75% for most patients. However significant challenges remain including developing better methods to predict which patients can be cured with less toxic treatment and which ones will benefit from augmented therapy. In addition, 25% of patients fail therapy and novel treatments that are focused on undermining specifically the leukemic process are needed urgently. In Section I, Dr. Carroll reviews current approaches to risk classification and proposes a system that incorporates well-established clinical parameters, genetic lesions of the blast as well as early response parameters. He then provides an overview of emerging technologies in genomics and proteomics and how they might lead to more rational, biologically based classification systems. In Section II, Drs. Mary Relling and Stella Davies describe emerging findings that relate to host features that influence outcome, the role of inherited germline variation. They highlight technical breakthroughs in assessing germline differences among patients. Polymorphisms of drug metabolizing genes have been shown to influence toxicity and the best example is the gene thiopurine methyltransferase (TPMT) a key enzyme in the metabolism of 6-mercaptopurine. Polymorphisms are associated with decreased activity that is also associated with increased toxicity. The role of polymorphisms in other genes whose products play an important role in drug metabolism as well as cytokine genes are discussed. In Sections III and IV, Drs. James Downing and Cheryl Willman review their findings using gene expression profiling to classify ALL. Both authors outline challenges in applying this methodology to analysis of clinical samples. Dr. Willman describes her laboratory's examination of infant leukemia and precursor B-ALL where unsupervised approaches have led to the identification of inherent biologic groups not predicted by conventional morphologic, immunophenotypic and cytogenetic variables. Dr. Downing describes his results from a pediatric ALL expression database using over 327 diagnostic samples, with 80% of the dataset consisting of samples from patients treated on a single institutional protocol. Seven distinct leukemia subtypes were identified representing known leukemia subtypes including: BCR-ABL, E2A-PBX1, TEL-AML1, rearrangements in the MLL gene, hyperdiploid karyotype (i.e., > 50 chromosomes), and T-ALL as well as a new leukemia subtype. A subset of genes have been identified whose expression appears to be predictive of outcome but independent verification is needed before this type of analysis can be integrated into treatment assignment. Chemotherapeutic agents kill cancer cells by activating apoptosis, or programmed cell death. In Section V, Dr. John Reed describes major apoptotic pathways and the specific role of key proteins in this response. The expression level of some of these proteins, such as BCL2, BAX, and caspase 3, has been shown to be predictive of ultimate outcome in hematopoietic tumors. New therapeutic approaches that modulate the apoptotic pathway are now available and Dr. Reed highlights those that may be applicable to the treatment of childhood ALL.