Translocation (8;21) Presenting As Severe Aplastic Anemia

Translocation of 8;21 (q22;q22), generating a fusion of RUNX1 and AML1 genes is considered leukemia-defining and typically presents as an unequivocal acute myeloid leukemia (AML) with peripheral blood blasts and a hypercellular marrow, although it has been reported in patients with Fanconi anemia and myelodysplastic syndrome (MDS) (Quentin S et al. Blood 2011 Apr 14;117(15)). Aplastic anemia is a rare disease characterized by severe pancytopenia and a hypocellular marrow. A few cytogenetic abnormalities, namely trisomy 8 and monosomy 7, are associated with particularly refractory aplastic anemia, and monosomy 7 is associated with clonal evolution to MDS and rapid progression to AML. We describe a case of newly-acquired severe aplastic anemia in a 23 year old woman. Laboratory studies at presentation showed white blood cells 1.38 k/uL, absolute neutrophil count 0 k/uL, hemoglobin 7.4 g/dL, absolute reticulocyte count 5 k/uL, and platelets 38 k/uL. Bone marrow biopsy was 5% cellular with trilineage hematopoiesis and absolutely no dysplasia, even on repeated review. Initial cytogenetic analysis performed outside the NIH at presentation was normal. The patient was transferred to our institution and promptly received standard immunosuppressive therapy given the severity of neutropenia. However, a repeat bone marrow analysis performed immediately prior to immunosuppression showed t(8:21) (q22;q22) by standard cytogenetics in 3 out of 20 metaphases, with confirmation by fluorescence in situ hybridization (FISH). Blasts were not identified despite multiple repeat bone marrow aspirations utilizing immunohistochemistry and flow cytometry. Testing for Fanconi anemia was negative and leukocyte telomere length was normal for age. She remained severely pancytopenic and transfusion dependent for many months. Chemotherapy for AML was withheld given the severe pancytopenia and absence of blasts, and a search for a bone marrow transplant donor was initiated. Progression to frank leukemia with circulating blasts occurred 8 months following initial presentation, just prior to unrelated donor allogeneic stem cell transplantation. To our knowledge, this is the first reported case of acquired severe aplastic anemia, profound marrow hypocellularity, hypocellular MDS or hypocellular AML occurring in association with the t(8;21)(q22;q22).

This unusual case prompted us to perform comparative genomic hybridization (CGH) using the single nucleotide polymorphism (SNP) based CytoScan high density microarrays on DNA from the patient’s bone marrow mononuclear cells. We detected multiple, large regions of copy neutral loss of heterozygosity (also referred to as uniparental disomy) in the patient’s marrow, ranging in size from 3 to 29 Mbp on multiple chromosomes. We hypothesized that the copy-neutral loss of heterozygosity observed in this case would not be present in other patients with acquired aplastic anemia at diagnosis or in normal controls. CGH did not demonstrate any large regions of copy neutral loss of heterozygosity in 10 patients with acquired severe aplastic anemia and normal cytogenetics at diagnosis, nor in 35 healthy controls. Emerging data show that SNP arrays can detect abundant copy neutral loss of heterozygosity amongst select hematologic malignancies and are associated with the duplication of oncogenic mutations. In our patient, copy neutral loss of heterozygosity possibly provided a second lesion, in addition to the RUNX1/AML1 abnormality, that facilitated initiation or progression to leukemia. These results suggest SNP based CGH arrays may be useful in distinguishing hypocellular AML from aplastic anemia and further studies utilizing this technology are warranted.