Acute Erythroleukemia M6

Erythroleukemia accounts for 4 to 5 percent of de novo and 10 to 20 percent of therapy-induced AML (t-AML). In 1976 the FAB cooperative group included erythroleukemia with the classification system of AML as M6 and agreed on a quantitative standard to be used in the diagnosis.14 The standards were revised in 19 8 5.58 The proposed criteria for the diagnosis of M6 are different from those used for the other types of AML. A minimum of 30 percent blasts among the nonerythroid cells (NECs) and more than 50 percent erythroid precursors with dysplastic features are necessary for diagnosis (Plate 14-18). Ringed sider-oblasts are present. The erythroid proliferation is often mega-loblastoid. PAS stain can demonstrate diffuse or blue staining of the cytoplasm. Despite the FAB classification M6 remained a point of controversy. Several studies argued for the evaluation of pronormoblasts in the diagnosis of M6.91 In 1992, Kowal-Vern and collegues92 proposed that erythroleukemia with greater than or equal to 30 percent pronormoblasts be incorporated into the FAB classification since its behavior is more consistent with AML than an MDS. As defined by the WHO,93 there are two types of acute erythroid leukemia. The first type called "ery-throid/myeloid" (FAB-M6a) is defined as having > 50 percent erythroid precursors in the bone marrow aspirate and > 20 percent myeloblasts based on the nonerythroid rich leukemia (FAB-M6b) with > 80 percent of the marrow composed of immature cells of the erythroid lineage (proerythroblasts and basophilic erythroblasts) with no evidence of a significant or recognizable myeloblastic component94 (Plate 14-19). Recent studies revealed that calculating the proerythroblasts as a component of total bone marrow erythroid cells provides a complementary method for delineating the three subsets.95 Recent studies have also suggested that pure erythroid malignancies such as Di Guglielmo disease (DG), which was defined as more than 30 percent proerythroblasts in the absence of myeloblasts should be included in M6 since both M6 and DG shared some clinical and laboratory features, cytogenetic patterns, and poor prognosis.96 A review of cytogenetic analysis were similar96,97 in two respects: two-thirds of studied cases had complex chromosomal abnormalities involving three or more chromosomes and abnormalities involving chromosome 5 and/or 7 occurred in approximately 50 percent of patients.

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