Molecular monitoring of hematologic malignancies: current and future issues

Arsenic trioxide-based therapy of relapsed acute promyelocytic leukemia: registry results from the European LeukemiaNet

In 2008, a European registry of relapsed acute promyelocytic leukemia was established by the European LeukemiaNet. Outcome data were available for 155 patients treated with arsenic trioxide in first relapse. In hematological relapse (n=104), 91% of the patients entered complete hematological remission (CR), 7% had induction death and 2% resistance, 27% developed differentiation syndrome and 39% leukocytosis, whereas no death or side effects occurred in patients treated in molecular relapse (n=40). The rate of molecular (m)CR was 74% in hematological and 62% in molecular relapse (P=0.3). All patients with extramedullary relapse (n=11) entered clinical and mCR. After 3.2 years median follow-up, the 3-year overall survival (OS) and cumulative incidence of second relapse were 68% and 41% in hematological relapse, 66% and 48% in molecular relapse and 90 and 11% in extramedullary relapse, respectively. After allogeneic or autologous transplantation in second CR (n=93), the 3-year OS was 80% compared with 59% without transplantation (n=55) (P=0.03). Multivariable analysis demonstrated the favorable prognostic impact of first remission duration ⩾1.5 years, achievement of mCR and allogeneic or autologous transplantation on OS of patients alive after induction (P=0.03, P=0.01, P=0.01) and on leukemia-free survival (P=0.006, P<0.0001, P=0.003), respectively.

How I treat children and adolescents with acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL) is a rare subtype of acute myeloid leukaemia. The outcome of paediatric APL has improved substantially over the past 20 years; cure rates above 80% are expected when all-trans retinoic acid (ATRA) is given with anthracycline-based regimens. The presenting features of paediatric APL may include severe bleeding and thrombotic complications, which contribute to the high early death rate. The incidence of leucocytosis and the microgranular subtype is greater in paediatric than adult APL, and children experience greater ATRA-related toxicity. It is crucial to begin ATRA therapy and intensive platelet and fibrinogen replacement on first suspicion of APL. Recent risk-adapted therapeutic trials have shown that patients at greater risk of relapse benefit from the introduction of high-dose cytarabine during consolidation. Combination therapy with ATRA and arsenic trioxide provides very effective frontline treatment and may reduce the need for subsequent anthracycline therapy.

Diagnostic value of detecting fusion proteins derived from chromosome translocations in acute leukaemia

Clonal chromosomal abnormalities such as balanced translocations are characteristic features of several human leukaemias and have long been detected by conventional cytogenetics on banded metaphases. The advent of molecular biology techniques, advanced karyotyping and immunohistochemistry methods has not only allowed identification of gene involvement at altered chromosome sites and better knowledge of leukaemia pathogenesis, but also contributed important improvements in diagnosis of these heterogeneous diseases. Such novel diagnostic strategies are nowadays being increasingly used to improve leukaemia classification, and in several instances, they help to establish the most appropriate therapeutic strategy in individual patients. Moreover, at least two leukaemia-associated fusion proteins derived from chromosome translocation are specifically targeted by therapeutic approaches which result in significantly increased anti-leukaemia efficacy and reduced toxicity. In this chapter, we highlight the importance of identifying these genetic lesions at diagnosis in acute leukaemia. Further, we discuss briefly the clinical utility of detecting these alterations for prognostic assessment and evaluation of response to treatment.

Acute promyelocytic leukemia: a model for the role of molecular diagnosis and residual disease monitoring in directing treatment approach in acute myeloid leukemia

Acute promyelocytic leukemia (APL) is characterized by a number of features that underpin the need for rapid and accurate diagnosis and demand a highly specific treatment approach. These include the potentially devastating coagulopathy, sensitivity to anthracycline-based chemotherapy regimens, as well as unique responses to all-trans retinoic acid and arsenic trioxide that have revolutionized therapy over the last decade. The chromosomal translocation t(15;17) which generates the PML-RARalpha fusion gene has long been considered the diagnostic hallmark of APL; however, this abnormality is not detected in approximately 10% cases with successful karyotype analysis. In the majority of these cases, the PML-RARalpha fusion gene is still formed, resulting from insertion events or more complex rearrangements. These cases share the beneficial response to retinoids and favorable prognosis of those with documented t(15;17), underscoring the clinical relevance of molecular analyses in diagnostic refinement. In other cases of t(15;17) negative APL, various chromosomal rearrangements involving 17q21 have been documented leading to fusion of RARalpha to alternative partners, namely PLZF, NPM, NuMA and STAT5b. The nature of the fusion partner has a significant bearing upon disease characteristics, including sensitivity to retinoids and arsenic trioxide. APL has provided an exciting treatment model for other forms of AML whereby therapeutic approach is directed towards cytogenetically and molecularly defined subgroups and further modified according to response as determined by minimal residual disease (MRD) monitoring. Recent studies suggest that rigorous MRD monitoring, coupled with pre-emptive therapy at the point of molecular relapse improves survival in the relatively small subgroup of PML-RARalpha positive patients with 'poor risk' disease. Advent of 'real-time' quantitative RT-PCR technology seems set to yield further improvements in the predictive value of MRD assessment, achieve more rapid sample throughput and facilitate inter- and intra-laboratory standardization, thereby enabling more reliable comparison of data between international trial groups.