DETECTION OF P53 MUTATIONS IN HEMATOLOGICAL MALIGNANCIES - COMPARISONBETWEEN IMMUNOCYTOCHEMISTRY AND DNA ANALYSIS

The wild type p53 protein has a short half-life and cannot be detected by immunohistochemistry on tissue sections. Mutated p53, on the other hand, has a prolonged half-life and becomes detectable by this method , so that its detection by immunohistochemistry in solid tumors is alm ost synonymous with mutation. We assessed the value of immunocytochemi cal analysis of p53 protein on blood or bone marrow slides in the dete ction of p53 mutation in hematological malignancies, by comparison wit h single-stranded conformation polymorphism (SSCP) analysis of exons 4 to 10 of the P53 gene. One hundred and twenty eight patients with acu te myeloid leukemia (AML), acute lymphoid leukemia (ALL), myelodysplas tic syndromes (MDS), or chronic lymphocytic leukemia (CLL) were studie d by both methods. Immunocytochemistry showed detectable levels of int racellular p53 in 19 cases (including 2/19 AML, 2/21 ALL, 11/48 MDS, 4 /40 CLL). Staining by p53 antibodies was restricted to the nucelus of blasts in AML, ALL, and MDS, and of lymphocytes in CLL. In 16 of the 1 9 cases, SSCP analysis, followed by direct sequencing, showed a p53 mi ssense mutation in exons 4 to 8 of the gene. In the remaining three ca ses, where the number of cells stained by p53 antibodies was small, no p53 mutation could be detected. On the other hand, SSCP and sequence analysis identified a p53 mutation in two patients who had negative im munocytochemical findings. Both cases had a nonsense mutation, presuma bly leading to reduced levels of truncated p53. Thus, overall, immunoc ytochemistry and SSCP gave concordant results in 123 of the 128 (96%) patients analyzed. Our findings show that immunocytochemistry on blood and bone marrow smears is a sensitive method of p53 mutation detectio n in hematological malignancies, except in the rare patients with chai n-terminating mutations. Positive immunocytochemistry is found in some patients with normal SSCP findings, and could correspond to overexpre ssion of a non-mutated p53, but also to p53 mutation in a minor propor tion of the malignant cells, undetectable by SSCP.