p53 in breast carcinomas: Association between presence of mutation and immunohistochemical expression using a semiquantitative approach

The aim of this study was to evaluate the concordance between the presence of p53 mutations in breast carcinomas expressing the protein by immunohisto chemistry. A series of 60 breast carcinomas was evaluated by immunohistoche mistry using monoclonal antibodies against p53 protein (DO 7 and PAb 1801). Twenty cases classified as being positive for p53 according to the current approach (if 5% or more of neoplastic cells contained reaction product in the nucleus) were used for molecular studies. These cases were re-assessed semiquantitatively using a scoring system based on intensity and percentage of stained cells. DNA was phenol-chloroform extracted from microdissected normal and tumour cells obtained from formalin-fixed, paraffin-embedded tis sue sections. Mutations in the p53 gene were analysed by SSCP (single stran d conformational polymorphism) with primers covering exons 2-3 to 11. Ten o ut of the 20 p53-positive cases presented mutations detected by SSCP analys is. Mutations have been found in several exons ranging from exon 4 to exon 10. We observed a positive relationship between the presence of mutations a nd immunohistochemical evaluation of p53 protein expression using a semiqua ntitative scoring system. All cases with more than 2/3 stained tumour cells and strong intensity of staining exhibited p53 mutations. At variance, no p53 mutations were found in cases with less than 1/3 stained tumour cells a nd moderate intensity of staining. Therefore, only the identification of po sitivity for p53 detected by immunohistochemistry did not always reflect th e detection of p53 mutations in breast cancer, however the use of a semiqua ntitative approach seems to be useful as an indicator of the presence of mu tation.