P53 GENE-MUTATIONS AND EXPRESSION OF P53 AND MDM2 PROTEINS IN INVASIVE BREAST-CARCINOMA - A COMPARATIVE-ANALYSIS WITH CLINICOPATHOLOGICAL FACTORS

The aim of the study was to analyze p53 gene mutations and the express ion of p53 and mdm2 proteins in 31 randomly selected invasive breast c arcinomas. The results were then correlated with tumor grade, stage, e strogen receptor status, nodal status, and DNA ploidy. The expression of the proteins p53 and mdm2 was determined immunohistochemically usin g formalin-fixed, paraffin-embedded material. Screening for p53 mutati on involved analysis of the highly conserved regions of the p53 gene ( exons 5-9) by the polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) technique. PCR products with band shifts were directly sequenced. Immunohistochemical staining of p53 was positive in 9 cases (29.0 %), only 2 of which showed a p53 gene mutation. These were identified as a C --> G transversion at the second position of c odon 278 in exon 8 and an A --> G transition at the second position of codon 205 in exon 6. A third case with a mutation was observed (C --> T transition, position 1 of codon 250 in exon 7) that did not show p5 3 immunohistochemically. Of the 9 p53-positive tumors, 2 were moderate ly differentiated (grade II). The remaining tumors were poorly differe ntiated (7/9). By contrast, p53-negative carcinomas were well differen tiated (grade I) in most cases (P = 0.02). DNA cytometry in 8 of the 9 p53-positive carcinomas revealed an aneuploid stem line. The majority of the p53-negative tumors were diploid (P = 0.01). Mdm2 oncoprotein was detected in 10 tumors (32.2 %), 4 of which were p53-positive, incl uding the 3 with mutations. The grading of the mdm2-positive tumors wa s moderate or poor, G1 carcinomas were always noted to be mdm2-negativ e (P = 0.04). Overexpression of p53 protein is a complex mechanism and does not merely indicate the detection of mutations in the p53 gene. This study has shown that p53 expression correlates with tumor grade a nd DNA ploidy. Mdm2 expression was also associated with the tumor grad e. Immunohistological demonstration of the p53 protein alone is insuff icient as a basis for comment on the functional state of the p53 gene and gene product. The interrelation between recognition of the p53 pro tein and gene mutation needs more careful assessment to define their r oles in the control of neoplasia.