First report of t(8;21)(q22;q22) in a case of de novo acute monoblastic leukemia

CD163: a specific immunohistochemical marker for acute myeloid leukemia with monocytic differentiation

Acute myeloid leukemias (AMLs) with monocytic differentiation with or without recurring cytogenetic abnormalities have prognostic significance. Therefore, it is important to recognize such cases. Monocytic differentiation is identified by morphology and confirmed by cytochemical stains or flow cytometry. However, the materials for such analyses are not always available (air-dried aspirate smears, touch preparations, fresh cells). Thus, the utility of CD163, a hemoglobin scavenger molecule present on monocytes/macrophages, in identifying a monocytic component in AML in fixed, paraffin-embedded bone marrows was assessed. Using tissue microarrays, 31 cases of AML with monocytic differentiation and 35 cases without monocytic differentiation were evaluated in a blinded fashion for CD163 positivity and compared with CD68. Diagnoses were previously well established using cytochemistry and flow cytometry techniques. CD163 immunoreactivity was seen in 49% of AML cases with and 6% (2/35) without monocytic differentiation. CD68 was positive in 81% of AML cases with and 17% without monocytic differentiation. CD163 showed superior specificity for a monocytic component in AML compared with CD68 (94% vs. 83%). However, the suboptimal sensitivity (49%) limits its utility as a definitive marker of monocytic differentiation if negative in paraffin sections. These findings demonstrate that CD163 is helpful for the evaluation of a monocytic component in AML. When positive, correlation and evaluation for an associated recurring cytogenetic abnormality is warranted.

AML1 interconnected pathways of leukemogenesis

The AML1 transcription factor, identified by the cloning of the translocation t(8;21) breakpoint, is one of the most frequent targets for chromosomal translocations in leukemia. Furthermore, polysomies and point mutations can also alter AML1 function. AML1, also called CBF alpha 2, PEBP alpha 2 or RUNX1, is thus implicated in a great number of acute leukemias via a variety of pathogenic mechanisms and seems to act either as an oncogene or a tumor suppressor gene. Characterization of AML1 knockout mice has shown that AML1 is necessary for normal development of all hematopoietic lineages and alterations in the overal functional level of AML1 can have a profound effect on hematopoiesis. Numerous studies have shown that AML1 plays a vital role in the regulation of expression of many genes involved in hematopoietic cell development, and the impairment of AML1 function disregulates the pathways leading to cellular proliferation and differentiation. However, heterozygous AML1 mutations alone may not be sufficient for the development of leukemia. A cumulative process of mutagenesis involving additional genetic events in functionally related molecules, may be necessary for the development of leukemia and may determine the leukemic phenotype. We review the known AML1 target genes, AML1 interacting proteins, AML1 gene alterations and their effects on AML1 function, and mutations in AML1-related genes associated with leukemia. We discuss the interconnections between all these genes in cell signaling pathways and their importance for future therapeutic developments.

Detection of a t(8;21)(q22;q22) in a case of M5 acute monoblastic leukemia

Although the translocation (8;21) is the single most common structural rearrangement reported in acute myeloblastic leukemia (AML), it is rarely seen in AML FAB type M5. We describe a case of a 51-year-old male with a diagnosis of acute monoblastic leukemia (AML M5b with hemophagocytic component) whose karyotype showed at (8;21)(q22;22). To our knowledge, this is the first report of this translocation in an AML M5b. The t(8;21) has been associated with a good prognosis, but our patient suffered a fast and fatal evolution.