p53 expression in myeloid cells of myelodysplastic syndromes. Association with evolution of overt leukemia.

To assess p53 expression in the hematopoietic cells of the bone marrow in premalignant as well as malignant conditions, we examined immunohistochemically bone marrow biopsies from patients with myelodysplastic syndromes (MDS, n = 51), acute myeloid leukemia (n = 42) and as a nonneoplastic condition, aplastic anemia (n = 20) and samples from individuals who had no hematological disorder (control, n = 12). Nuclear accumulation of p53 protein was found in seven of 51 patients with MDS (14%) and two of 42 acute myeloid leukemia patients (5%), whereas patients with aplastic anemia and control subjects were uniformly negative for p53 protein. In the bone marrow of patient with MDS, p53-positive cells constituted about 5 to 30% of the total bone marrow cells. Two-color immunohistochemical analysis revealed that the p53-positive cells were also positive for the myeloid cell marker. Half of the MDS cases that evolved to overt leukemia (seven of 14) exhibited positive p53 reaction in the bone marrow at the time of initial diagnosis. This frequency (50%) was significantly higher than that in de novo acute myeloid leukemia cases. All of the seven MDS cases that exhibited p53 expression at the time of initial diagnosis developed overt leukemia later, and p53 expression was maintained throughout the progression of MDS. The results suggest that p53 mutations that occur in the myeloid cells in MDS may confer a growth advantage to these cells resulting in the progression to overt leukemia. Thus, immunohistochemical examination for p53 is very useful for predicting the evolution to overt leukemia from MDS.