The mutation of the nucleophosmin gene (NPM1) is the most frequently occurring genetic aberration in acute myeloid leukemia (AML). Due to the high frequency and the obvious impact on disease outcome, the current WHO classification also defines the new (provisory) entity of .,AML with NPM mutation". Mutations of NPM1 exon 12 affect both nuclear complexion and nuclear export signaling (NES) domain resulting in redistribution and accumulation of the NPM protein in the cytoplasm of leukaemic cells. The effect of gene mutation can be directly demonstrated by the occurrence of cytoplasmic NPM using immunohistochemistry (NPMc+). The present study focused on further biological and clinical characterization of NPMc+ AML determined by histological and cytological preparations of the bone marrow. 41 adult AML cases were investigated in our center between 2005 and 2008, 6/41 cases were presented with cytoplasmic NPM immunostaining (14,6%). All but one were female patients, and were diagnosed as de novo AML with no recurrent cytogenetic aberrations (6/23, 26,1%). The NPMc+ group displayed M2 or M4 morphology, low CD34, c-kit and HLA-DR expression making a clear phenotypic distinction from the unaffected cases possible. These results are in agreement with previous studies. In conclusion, immunohistochemistry is well applicable for the identification of NPM mutated AML in the daily hematopathology practice.
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