P-250 Nucleophosmin cytoplasmic and nucleus immunohistochemical cell positivity of bone marrow biopsy sections in AML and MDS patients

Abstract

Background Nucleophosmin (NPM) is phosphoprotein in nucleolus and shuttles continuously between nucleus and cytoplasm. Major role of NPM is to mediate nuclear export of ribosome components to the cytoplasm and to control centrosome duplication and it also interacts with oncosupressors p53 and p19Arf thus controlling cell proliferation and apoptosis. NPM mutations are involved in pathogenesis of some AML cases. Introduction The abnormal mutated NPM1 protein shows an aberrant cytoplasmic localization in leukemic cells (NPMc), whereas the wild-type protein is mainly located in the nucleolus and on the nuclear membrane. Approximately one-third of cases of denovo acute myeloblastic leukemia (AML) carry mutations in the c-terminal region of NPM (NPM1) gene. NPM1 mutations are rare in myelodisplasia (MDS) but in some reports NPM mutations and NPMc cell bone marrow cell positivity were also found in MDS. Purpose Aim of the study were to analyze cell NPM immunohistochemical expression in nuclei (NPMn) and cytoplasm (NPMc) in bone marrow (BM) sections of 7 patients with de novo AML and 9 MDS patients. Materials and Methods Immunohistochemical procedures were performed on paraffin sections cut from B5-fixed/EDTA-decalcified BM biopsies. Sections were subjected to micro waving/antigen retrieval, pH9 and immunostained with anti-NPM monoclonal antibody (clone 376) using immuno alkaline phosphatase technique. NPMc and NPMn cell positivity between AML and MDS patients were statistically compared with Mann-Whitney and Chi-square tests. From patients informed consent was obtained. Results NPMn cell positivity was seen in 6/7 AML and in 8/9 MDS patients. NPMc was detected in 5/7 AML and in 8 out of 9 MDS patients. Percentages of NPMn of BM cells were higher in MDS than in AML patients with borderline statistical significance. NPMn immunoexpression above 30% of BM positive cells was more frequently (with statistical significance) observed in MDS than in AML patients (p< 0.05). Conclusions Higher NPMn cell positivity (above 30% of nucleated BM cells) in MDS is probably linked to higher number of normal BM cells in MDS. Lower NPMn cell positivity in AML is maybe associated to higher number of leukemic cells and also to NPM functional loss in progression and transformation of MDS to AML. NPMc was also observed in most of our AML and MDS patients. This finding is in a concordance with some recent reports also implicating that that NPM1 mutations may be also seen in MDS, but further studies are needed to analyze correlation of NPMc cell positivity and NPM1 mutations in MDS patients