A case of acute eosinophilic granulocytic leukemia with PML-RAR alpha fusion gene expression and response to all-trans retinoic acid

Uncommon phenotypes of acute myelogenous leukemia: basophilic, mast cell, eosinophilic, and myeloid dendritic cell subtypes: a review

The potential of the transformed (leukemic) multipotential hematopoietic cell to differentiate and mature along any myeloid lineage forms the basis for the phenotypic classification of acute and chronic myelogenous leukemia. Although most cases of leukemia can be classified phenotypically by the dominant lineage expressed, the genotype within each phenotype is heterogeneous. Thus, covert genetic factors, cryptic mutations, and/or polymorphisms may interact with the seminal transforming genetic mutations to determine phenotype. The phenotype usually is expressed sufficiently to determine the lineage that is dominant in the leukemic clone by light microscopic examination, by cytochemistry of blood and marrow cells, and by immunophenotyping. The basis for the frequency of the AML phenotypes is unclear, although there is a rough concordance with the frequency of marrow precursor cells of different lineages. The least common AML phenotypes are a reflection of the least common blood or marrow cell lineages: acute basophilic, acute mast cell, acute eosinophilic, and acute myeloid dendritic cell leukemia. We discuss the features of these uncommon phenotypes and review the criteria used for their diagnosis.

Morphological and cytochemical characteristics of leukaemic promyelocytes

Evaluation of cell morphology is usually sufficient to diagnose acute promyelocytic leukaemia (APL). In this chapter we discuss the features of classical hypergranular APL, the APL variant, hyperbasophilic promyelocytic leukaemia, APL with basophil-like granules, acute eosinophilic leukaemia with PML/RARalpha positivity and the morphology of APL cells lacking t(15;17). In addition to morphological examination, cytochemical investigations (peroxidase chloroacetate-esterase, etc.) may help further in defining the cytology of leukaemic cells in APL.

Molecular cytogenetic characterization and clinical relevance of additional, complex and/or variant chromosome abnormalities in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by typical morphological manifestation, t(15;17) translocation and active response to all-trans retinoic acid (ATRA) in the great majority of patients. However, a subset of APL cases may present atypical phenotypic, cytogenetic or molecular features at different stages of the disease. The biological and clinical significance of these features sometimes remains obscure. In this study, 284 APL patients were cytogenetically analyzed and precise diagnosis was performed according to the molecular cytogenetic results. Twenty-six APL patients were identified as having additional, complex and/or variant chromosomal abnormalities at diagnosis or at relapse, 16 of them being further analyzed using fluorescence in situ hybridization (FISH) or chromosome painting (CP). Interestingly, some of these chromosomal aberrations were found to be associated with atypical morphology and/or drug response, indicating a genotype-phenotype correlation. Analysis of the complex karyotype may also allow a better understanding of the levels of cellular origin of the leukemogenesis. Examination of the remission induction and survival data showed that the presence of the additional/complex chromosome abnormalities was related to the prognosis in both primarily diagnosed and relapsed patients in this series.

Extramedullary disease in acute promyelocytic leukemia

All-trans retinoic acid (ATRA) is currently recommended as standard treatment for acute promyelocytic leukemia (APL). However there has been increasing concern that ATRA is associated with unusual sites of relapse. Although there is insufficient evidence so far to substantiate this, we review the potential mechanisms by which ATRA may increase the incidence of extramedullary and, in particular, central nervous system (CNS) relapse.

Morphology of acute promyelocytic leukemia with cytogenetic or molecular evidence for the diagnosis: characterization of additional microgranular variants

Early diagnosis of t(15;17) acute promyelocytic leukemia (APL) is essential because of the associated disseminated intravascular coagulation and the unique response of the disease to all-trans retinoic acid (ATRA) therapy. Early diagnosis depends primarily on morphological recognition. The French-American-British (FAB) classification, however, does not describe all morphological variations that occur in APL. In 25 cases with evidence of APL confirmed by cytogenetic and/or molecular analysis, we found a heterogeneous morphological group. The most common form of APL was heterogeneous and consisted of various combinations of cells in which hypergranular cells and some cells with multiple Auer rods were obvious. In some cases, one cell predominated. This led to the description of five subcategories. These included the classical FAB M3 with hypergranular cells and multiple Auer rods; the FAB variant with hypogranular bilobed cells; the basophilic cell type of McKenna et al. [Br. J. Haematol 50:201, 1982]; and two additional subtypes, one consisting of differentiated promyelocytes and a few blast cells (M2-like), and the other consisting largely of blast cells and a few early promyelocytes (M1-like). Immunophenotyping revealed a pattern of CD33 and/or CD13 positivity, and CD14 and HLA-DR negativity in 96% of cases. CD2 was positive in the FAB variant and in the subtype with basophilic cells, but negative with other subtypes. Three out of five cases with basophilic cell predominance [McKenna et al.: Br J Haematol 50:201, 1982], and one out of two M2-like cases, responded to ATRA therapy. Awareness of the heterogeneity and the atypical morphologic subtypes found in t(15;17) APL will contribute to improved recognition and early institution of ATRA therapy.

Acute promyelocytic leukemia: cellular and molecular basis of differentiation and apoptosis

Acute promyelocytic leukemia (APL) accounts for about 10% of all acute myeloid leukemias and is characterized by the chromosomal translocation t(15;17), which fuses the retinoic acid receptor (RAR) alpha gene to the promyelocytic leukemia (PML) gene. The PML-RAR alpha fusion gene plays an important role in leukemogenesis through antagonizing retinoic acid signalling and the regulatory pathways mediated by PML. APL is the first example of a human cancer that can be effectively treated with the differentiation inducer all-trans retinoic acid (ATRA). The therapeutic effect of ATRA in APL has been associated with the direct modulation of PML-RAR alpha, the restoration of the differentiation pathways regulated by wild-type RAR/retinoid X receptor heterodimer and PML. More recently, a second drug, arsenic trioxide (As2O3), has been discovered in China that also has a strong therapeutic effect against APL. As2O3 can induce clinical remission in de novo or relapsed APL patients and has no cross-resistance with ATRA. It has dual effects on APL cells: preferential apoptosis at high concentration (0.5-2 microM) and partial differentiation at low concentration (0.1-0.5 microM). Modulation and degradation of PML-RAR alpha proteins can be induced by As2O3 and probably contribute to these two effects. These studies lead to a model in which PML-RAR alpha could be the target of both ATRA differentiation therapy and As2O3 apoptosis therapy.