Immunohistochemical detection of p53, mdm2, waf1/p21, and Ki67 proteins in bone marrow biopsies in myelodysplastic syndroms, acute myelogenous leukaemias and chronic myeloproliferative disorders.

The aim oof this study was to investigate the immunohistochemical expression of p53, mdm2, and waf1/p21 proteins in myelodysplastic syndromes (MDS), acute myelogenous leukaemias (AML), and chronic myeloproliferative disorders (CMPD). Paraffin-sections of bone marrow biopsies from 30 cases of MDS (6 cases of RAEB and RAEB-T) 22 AML (4 cases occurring in the setting of MDS), 16 chronic myeloproliferative disorders (CMPD), and 10 cases without alterations were investigated by immunohistochemistry for p53, waf1/p21, mdm2 and Ki67 proteins. P53 was detected in immature myeloid cells in 6/30 MDS (20%) and in 6/22 AML (27%) while it was not expressed in CMPD. Of the 6 p53 positive AML, 3 occurred as evolution of MDS and 3 were de novo acute leukaemias. Waf1/p21 was detected in 5/22 (23%) AML in immature myeloid cells. Waf1/p21 was also expressed in 18/30 (60%) MDS and 10/16 (63%) CMPD in variable proportion (5-25%) of the mature myeloid cells and megakaryocytes. Waf1/p21 was not detected in immature myeloid cells in MDS and CMPD. Mdm2 protein was expressed in 3/30 (10%) MDS in the immature myeloid cells and in 1/22 AML in blastic cells. The combined immunophenotypes of immature myeloid cells of MDS were: p53+/mdm2+/waf1-: 3, p53+/mdm2-/waf1-: 3, while the immunohistochemical patterns of AML were: p53+/mdm2-/waf1-: 4, p53+/mdm2+/waf1+: 1, p53+/mdm2-/waf1+: 1, p53-/mdm2-/waf1+: 3. Ki67/MIB1 staining was found in at least 30% of immature myeloid cells in MDS and AML and in at least 20% of these cells in CMPD. In conclusion, our results indicate that p53 protein is overexpressed in the myeloid lineage in a proportion of AML and MDS, while is not detected in CMPD and normal bone marrow, p53 expression was much more frequent in AML occurring as an evolution of MDS than in de novo AML. The combined immunophenotypes of p53 positive AML and MDS suggest that p53 overexpression may be due to mutation, in some AML and MDS cases with the p53+/mdm2-/waf1- phenotype. However, it would be also possible that p53 protein accumulation is not related to p53 mutation but to inhibition of p53/mdm2 binding due to mdm2 defects and/or other events related to cell stress signals. On the other hand, waf1/p21 protein overexpression without p53 expression in some AML could be p53-independent and may represent an attempt to control the high proliferation rate which was evidenced by Ki67/MIB1 immunostaining. However, the possibility of p21 to arrest cell-cycle, in these cases of AML, seems to be overridden, suggesting that cell-cycle deregulation may be involved in a proportion of AML.