Genetic tests to evaluate prognosis and predict therapeutic response in acute myeloid leukemia

Management of patients with acute myeloid leukemia relies on genetic tests that inform diagnosis and prognosis, predict response to therapy, and measure minimal residual disease. The value of genetics is reinforced in the revised 2008 World Health Organization acute myeloid leukemia classification scheme. The various analytic procedures-karyotype, fluorescence in situ hybridization, reverse transcription polymerase chain reaction, DNA sequencing, and microarray technology-each have advantages in certain clinical settings, and understanding their relative merits assists in specimen allocation and in effective utilization of health care resources. Karyotype and array technology represent genome-wide screens, whereas the other methods target specific prognostic features such as t(15;17) PML-RARA, t(8;21) RUNX1-RUNX1T1, inv(16) CBFB-MYH11, 11q23 MLL rearrangement, FLT3 internal tandem duplication, or NPM1 mutation. New biomarkers and pharmacogenetic tests are emerging. The pathologist's expertise is critical in 1) consulting with clinicians about test selection as well as specimen collection and handling; 2) allocating tissue for immediate testing and preserving the remaining specimen for any downstream testing that is indicated once morphology and other pertinent test results are known; 3) performing tests that maximize outcome based on the strengths and limitations of each assay in each available specimen type; and 4) interpreting and conveying results to the rest of the health care team in a format that facilitates clinical management. Acute myeloid leukemia leads the way for modern molecular medicine.

Strikingly different molecular relapse kinetics in NPM1c, PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11 acute myeloid leukemias

Early relapse detection in acute myeloid leukemia is possible using standardized real-time quantitative polymerase chain reaction (RQ-PCR) protocols. However, optimal sampling intervals have not been defined and are likely to vary according to the underlying molecular lesion. In 74 patients experiencing hematologic relapse and harboring aberrations amenable to RQ-PCR (mutated NPM1 [designated NPM1c], PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11), we observed strikingly different relapse kinetics. The median doubling time of the CBFB-MYH11 leukemic clone was significantly longer (36 days) than that of clones harboring other markers (RUNX1-RUNX1T1, 14 days; PML-RARA, 12 days; and NPM1c, 11 days; P < .001). Furthermore, we used a mathematical model to determine frequency of relapse detection and median time from detection of minimal residual disease to hematologic relapse as a function of sampling interval length. For example, to obtain a relapse detection fraction of 90% and a median time of 60 days, blood sampling every sixth month should be performed for CBFB-MYH11 leukemias. By contrast, in NPM1c(+)/FLT3-ITD(-), NPM1c(+)/FLT3-ITD(+), RUNX1-RUNX1T1, and PML-RARA leukemias, bone marrow sampling is necessary every sixth, fourth, and fourth and second month, respectively. These data carry important implications for the development of optimal RQ-PCR monitoring schedules suitable for evaluation of minimal residual disease-directed therapies in future clinical trials.

Evidence for direct involvement of epirubicin in the formation of chromosomal translocations in t(15;17) therapy-related acute promyelocytic leukemia

Therapy-related acute promyelocytic leukemia (t-APL) with t(15;17)(q22;q21) involving the PML and RARA genes is associated with exposure to agents targeting topoisomerase II (topoII), particularly mitoxantrone and epirubicin. We previously have shown that mitoxantrone preferentially induces topoII-mediated DNA damage in a "hotspot region" within PML intron 6. To investigate mechanisms underlying epirubicin-associated t-APL, t(15;17) genomic breakpoints were characterized in 6 cases with prior breast cancer. Significant breakpoint clustering was observed in PML and RARA loci (P = .009 and P = .017, respectively), with PML breakpoints lying outside the mitoxantrone-associated hotspot region. Recurrent breakpoints identified in the PML and RARA loci in epirubicin-related t-APL were shown to be preferential sites of topoII-induced DNA damage, enhanced by epirubicin. Although site preferences for DNA damage differed between mitoxantrone and epirubicin, the observation that particular regions of the PML and RARA loci are susceptible to these agents may underlie their respective propensities to induce t-APL.

Real-time quantitative polymerase chain reaction detection of minimal residual disease by standardized WT1 assay to enhance risk stratification in acute myeloid leukemia: a European LeukemiaNet study

PURPOSE

Risk stratification in acute myeloid leukemia (AML) is currently based on pretreatment characteristics. It remains to be established whether relapse risk can be better predicted through assessment of minimal residual disease (MRD). One proposed marker is the Wilms tumor gene WT1, which is overexpressed in most patients with AML, thus providing a putative target for immunotherapy, although in the absence of a standardized assay, its utility for MRD monitoring remains controversial.

PATIENTS AND METHODS

Nine published and in-house real-time quantitative polymerase chain reaction WT1 assays were systematically evaluated within the European LeukemiaNet; the best-performing assay was applied to diagnostic AML samples (n = 620), follow-up samples from 129 patients treated with intensive combination chemotherapy, and 204 normal peripheral blood (PB) and bone marrow (BM) controls.

RESULTS

Considering relative levels of expression detected in normal PB and BM, WT1 was sufficiently overexpressed to discriminate > or = 2-log reduction in transcripts in 46% and 13% of AML patients, according to the respective follow-up sample source. In this informative group, greater WT1 transcript reduction after induction predicted reduced relapse risk (hazard ratio, 0.54 per log reduction; 95% CI, 0.36 to 0.83; P = .004) that remained significant when adjusted for age, WBC count, and cytogenetics. Failure to reduce WT1 transcripts below the threshold limits defined in normal controls by the end of consolidation also predicted increased relapse risk (P = .004).

CONCLUSION

Application of a standardized WT1 assay provides independent prognostic information in AML, lending support to incorporation of early assessment of MRD to develop more robust risk scores, to enhance risk stratification, and to identify patients who may benefit from allogeneic transplantation.

Independent prognostic factors for AML outcome

Over the last three decades there have been dramatic advances in deciphering the cytogenetic and molecular lesions underlying the pathogenesis of acute myeloid leukemia (AML). These have not only afforded greater insights into disease biology, but also provided useful information predicting the likelihood of any given patient achieving and maintaining remission following conventional chemotherapy, leading to the development of risk-stratified treatment approaches. However, it is becoming increasingly apparent that AML is highly heterogeneous at the molecular level. Defining the individual genetic abnormalities or combinations of markers that provide significant independent prognostic information and establishing their respective relationships to other pre-treatment characteristics that impact on outcome, such as age and presenting white blood cell count, presents a major ongoing challenge. Moreover, there is increasing evidence that risk of relapse and overall survival can be predicted by assessment of kinetics and depth of response following front-line therapy and monitoring of the leukemic burden using molecular or immunological approaches to minimal residual disease (MRD) detection. These advances present the exciting prospect that panels of pre-treatment parameters affording independent prognostic information can be integrated with precise measurement of treatment response using MRD technologies to provide greater refinement in risk-adapted management of AML. This could lead to further improvements in outcome and serve to identify in a more reliable fashion those patients most likely to benefit from allogeneic transplant in first remission.

Management of acute promyelocytic leukemia: recommendations from an expert panel on behalf of the European LeukemiaNet

The introduction of all-trans retinoic acid (ATRA) and, more recently, arsenic trioxide (ATO) into the therapy of acute promyelocytic leukemia (APL) has revolutionized the management and outcome of this disease. Several treatment strategies using these agents, usually in combination with chemotherapy, but also without or with minimal use of cytotoxic agents, have provided excellent therapeutic results. Cure of APL patients, however, is also dependent on peculiar aspects related to the management and supportive measures that are crucial to counteract life-threatening complications associated with the disease biology and molecularly targeted treatment. The European LeukemiaNet recently appointed an international panel of experts to develop evidence- and expert opinion-based guidelines on the diagnosis and management of APL. Together with providing current indications on genetic diagnosis, modern risk-adapted front-line therapy and salvage treatment, the review contains specific recommendations for the identification and management of most important complications such as the bleeding disorder, APL differentiation syndrome, QT prolongation and other ATRA- and ATO-related toxicities, as well as for molecular assessment of response to treatment. Finally, the approach to special situations is also discussed, including management of APL in children, elderly patients, and pregnant women.