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  • Tommie Benjamin posted an update 4 months, 1 week ago

    DiscussionChronic myelogenous leukemia (CML) is a clonal disorder involving the pluripotent stem cell and is consistently associated with the BCR-ABL1 fusion gene located on the Philadelphia chromosome [1]. The disease typically evolves in 3 distinct clinical stages: chronic and accelerated phases and blast crisis. In approximately 70% of cases, the blast lineage is myeloid, of which granulocytic and monocytic blasts are more common. The remaining 20–30% of cases show lymphoblast proliferation. Erythroid blast phase of CML is relatively rare and a literature review suggests that the incidence ranges from 0% to 10% [2].Acute erythroid leukemia is a rare subtype (50% of the entire nucleated cell population), may frequently show a shift to immaturity, are dyspoietic and myeloblasts comprise greater than 20% of non-erythroid mm molarity [1].Chronic myelogenous leukemia with erythroid crisis is a rare entity with variable reported incidence rates [2]. Based on our review of literature we came across very few reported cases of transformation of underlying CML to acute erythroid leukemia [3–8]. We also searched our institutional database for all cases of CML that transformed to acute leukemia over the course of last twenty years and did not find any other CML patient with erythroid blast crisis. Whether the criteria listed for diagnosis of erythroleukemia should be applied in CML erythroid blast phase is poorly defined. Some studies have considered the percentage of normoblasts below 50% as criteria for erythroblast phase but not erythroleukemia [6]. Although acute erythroid leukemia is far less common than CML erythroblast crisis, a few cases of Philadelphia-positive acute erythroid leukemia have been reported [5]. Studies have also suggested that erythroid blast phase is not independent of CML chronic phase. McFarlane and Tseih [6] were able to demonstrate a ‘bcr-abl’ fusion product in the normoblasts of CML, which provides concrete evidence confirming erythroid leukemia rather than a hyperplastic process. In our case at the time of disease progression in 2015 we were able to demonstrate presence of both bcr-abl fusion and monosomy 7 in majority of the bone marrow cells that on morphology were mostly erythroid precursors by FISH assays. Although the 9; 22 translocation was seen at the time of diagnosis, the anomalies of chromosome 7 and 3 were newly acquired in 2015, indicating karyotype evolution and disease progression. In the blastic phase of CML, several additional chromosome aberrations in addition to the Philadelphia chromosome have been reported in 75–80% of patients [3,5,7]. Complex rearrangements are widely dominant in acute erythroleukemia with clonal abnormalities mostly involving chromosomes 5 and 7 followed by 8, 16 and 21 [3]. There is no chromosome abnormality specific to erythroleukemia. In our patient we found anomalies of chromosomes 3 and 7 as her disease progressed.pH-positive acute erythroid leukemia represents an even less common occurrence than erythroid blast phase CML. It is difficult to distinguish the erythroblast phase of CML from a pH-positive acute leukemia [9]. Although complex karyotype and presence of multiple chromosomal abnormalities is fairly common in all cases of acute erythroleukemia, very few cases of pH-positive erythroleukemia have been reported [5]. Blast phase of CML is often associated with a complex karyotype, including trisomy 8 and 19, double pH chromosomes, and isochromosome i (17q) [10,11]. The WHO classification does not specifically address the issue of erythroid hyperplasia in patients with CML or erythroid blast phase of CML. We feel due to presence of more than 50% erythroid precursors and increased myeloblasts (greater than 20% of the non-erythroid cells) our case meets the WHO diagnostic criteria for acute erythroleukemia (erythroid/myeloid). The criteria for diagnosing acute erythroleukemia arising from an underlying CML have not been firmly established, partly due to the rare occurrence of this phenomenon.

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