Inversion 16 and translocation (16;16) in ANLL M4eo break in the same subregion of the short arm of chromosome 16

Clinical and prognostic significance of eosinophilia and inv(16)/t(16;16) in pediatric acute myelomonocytic leukemia (AML-M4)

BACKGROUND

The cytogenetic aberrations inv(16)(p13.1q22)/t(16;16)(p13.1;q22), frequently detected in acute myelomonocytic leukemia with eosinophilia (FAB type M4eo), are generally considered a prognostically favorable subgroup. M4eo comprises a distinct morphology compared to M4 without eosinophilia (M4eo-) and therefore may be indicative for a different pathogenesis.

PROCEDURES

Morphology and cytogenetic/molecular analyses of a Dutch cohort of pediatric acute myelomonocytic leukemia (AML-M4) patients were performed and studied in order to analyze the association between the presence of eosinophilia morphology (M4eo+), inv(16)/t(16;16) (inv(16)+), clinical features, and outcome.

RESULTS

Of the 119 included patients with available combined morphological and cytogenetic results, 60% had M4eo- without inv(16) (inv(16)-), 10% had M4eo-/inv(16)+, 13% had M4eo+/inv(16)-, and 17% had M4eo+/inv(16)+. M4eo+ was significantly associated with the presence of inv(16)/t(16;16) (P < 0.001). Patients with M4eo+ had no significantly superior outcome compared with patients with M4eo-, whereas patients with inv(16)+ had significantly superior probabilities of event-free survival and probabilities of overall survival compared with patients without inv(16)-. Patients with M4eo+/inv(16)+ had no significantly better outcome than those with M4eo-/inv(16)+.

CONCLUSION

The prognostically favorable impact of distinct morphology with eosinophilia probably relies on its association with inv(16)/t(16;16). Simultaneous presence of both eosinophilia and inv(16) was not associated with superior outcome in our study. These results may be relevant for risk-group classification and risk-group adapted treatment and underline the importance of accurate cytogenetic analysis.

Proleukemic RUNX1 and CBFbeta mutations in the pathogenesis of acute leukemia

The existence of non-random mutations in critical regulators of cell growth and differentiation is a recurring theme in cancer pathogenesis and provides the basis for our modern, molecular approach to the study and treatment of malignant diseases. Nowhere is this more true than in the study of leukemogenesis, where research has converged upon a critical group of genes involved in hematopoietic stem and progenitor cell self-renewal and fate specification. Prominent among these is the heterodimeric transcriptional regulator, RUNX1/CBFbeta. RUNX1 is a site-specific DNA-binding protein whose consensus response element is found in the promoters of many hematopoietically relevant genes. CBFbeta interacts with RUNX1, stabilizing its interaction with DNA to promote the actions of RUNX1/CBFbeta in transcriptional control. Both the RUNX1 and the CBFbeta genes participate in proleukemic chromosomal alterations. Together they contribute to approximately one-third of acute myelogenous leukemia (AML) and one-quarter of acute lymphoblastic leukemia (ALL) cases, making RUNX1 and CBFbeta the most frequently affected genes known in the pathogenesis of acute leukemia. Investigating the mechanisms by which RUNX1, CBFbeta, and their proleukemic fusion proteins influence leukemogenesis has contributed greatly to our understanding of both normal and malignant hematopoiesis. Here we present an overview of the structural features of RUNX1/CBFbeta and their derivatives, their roles in transcriptional control, and their contributions to normal and malignant hematopoiesis.

Pathogenesis of acute myeloid leukaemia and inv(16)(p13;q22): a paradigm for understanding leukaemogenesis?

Acute myeloid leukaemia (AML) has been proposed to arise from the collaboration between two classes of mutation, a class I, or proliferative, mutation and a class II, or blocking, mutation. A limitation of this so-called 'two-hit' hypothesis has been the lack of identifiable proliferative and blocking mutations in most AML cases. However, it is now known that the CBFbeta-MYH11 fusion gene in AML and inv(16), by disrupting the normal transcription factor activity of core binding factor (CBF), functions as a class II mutation. In addition, nearly 70% of patients with AML and inv(16) are known to possess mutually exclusive mutations of the receptor tyrosine kinases (RTKs), c-KIT and FLT3, as well as RAS genes, that provide a class I, or proliferative, signal. AML and inv(16), therefore, is one of the best understood of the acute leukaemias at the genetic level and so provides a paradigm for the 'two-hit' hypothesis of leukaemogenesis. This paper reviews the recent advances in the molecular pathology of AML and inv(16) and discusses possible therapeutic implications of the current pathogenetic model.

Inversion-associated translocations in acute myelomonocytic leukemia with eosinophilia

Cytogenetic studies of three acute myelomonocytic leukemias with bone marrow eosinophilia (M4EO) revealed chromosome 16 inversion associated with additional abnormalities. The inverted chromosome 16 was involved in two patients. Fluorescence in situ hybridization (FISH) experiments with a YAC probe detecting inv(16) showed that the translocation breakpoints involving chromosome 16 did not implicate the inversion breakpoints. FISH can thus distinguish between true variant translocations and translocations with other breakpoints on chromosome 16 in M4EO.

Statistical methods in interphase cytogenetics: an experimental approach

In situ hybridization (ISH) techniques on interphase cells, or interphase cytogenetics, have powerful potential clinical and biological applications, such as detection of minimal residual disease, early relapse, and the study of clonal evolution and expansion in neoplasia. Much attention has been paid to issues related to ISH data acquisition, i.e., the numbers, colors, intensities, and spatial relationships of hybridization signals. The methodology concerning data analysis, which is of prime importance for clinical applications, however, is less well investigated. We have studied the latter for the detection of small monosomic and trisomic cell populations using various mixtures of human female and male cells. With a chromosome X specific probe, the male cells stimulated monosomic subpopulations of 0, 1, 5, 10, 50, 90, 95, 99, and 100%. Analogously, when a (7 + Y) specific probe combination was used, containing a mixture of chromosome No. 7 and Y-specific DNA, the male cells simulated trisomic cell populations. Probes specific for chromosomes Nos. 1, 7, 8, and 9 were used for estimation of ISH artifacts. Three statistical tests, the Kolmogorov-Smirnov test, the multiple-proportion test, and the z'-max test, were applied to the empirical data using the control data as a reference for ISH artifacts. The Kolmogorov-Smirnov test was found to be inferior for discrimination of small monosomic or trisomic cell populations. The other two tests showed that when 400 cells were evaluated, and using selected control probes, monosomy X could be detected at a frequency of 5% aberrant cells, and trisomy 7 + Y at a frequency of 1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical aspects of acute myeloid leukemias of the FAB types M3 and M4Eo. The AML Cooperative Group

Acute promyelocytic leukemia (AML FAB M3, APL) and acute myelomonocytic leukemia with abnormal eosinophils (AML M4Eo) are considered distinct entities with characteristic clinical, morphological, cytogenetic, and prognostic features. Promyelocytic leukemia is characterized by abnormal promyelocytes replacing normal hematopoiesis associated with a translocation between the long arms of chromosomes 15 and 17 t (15; 17), severe coagulopathy, and responsiveness to all-trans retinoic acid (tretinoin). Characteristic features of AML M4Eo are a myelomonocytic marrow infiltration, eosinophils with abnormal immature granules positive for chloroacetate esterase, an inversion or translocation of chromosome 16, and an increased risk of meningeal relapses. Prognosis of both types of AML has been reported to be better than prognosis of the other entities combined. Since most of the published data were collected from heterogeneous patient populations treated with various chemotherapeutic regimens, we have analyzed treatment outcome of AML M3 and M4Eo in the AMLCG-85 study for patients younger than 60 years. For the total population of 594 patients of this study, CR rate was 68.89%, early death rate 11.60%, and no or partial remission was achieved in 19.51% of the cases. Of 40 patients with AML M3 or M3 v complete remission was attained in 62.5%. Nine patients died within 42 days after the start of antileukemic therapy (22.5%). Of these nine, four died because of infection, five because of bleeding. Relapse-free survival rate was 59% after 3 years, significantly better than the respective curve of the other FAB types combined (35% after 3 years). In AML M4Eo, 91.7% of the 24 patients reached complete remission. The early death rate was 8.3%. No case of nonresponse was seen. Relapse-free survival rate was 49% after 3 years compared with 35% for the other types combined.