Breast cancer is the most common cancer in women in the western world. Two of the most frequently occuring chromosomal abnormalities in human breast carcinoma are the loss of p53 tumour suppressor gene function and the amplification of the c-erbB2 oncogene. Previous studies have demonstrated the role of p53 gene product in the maintenance of chromosomal stability and the correlation between c-erbB2 amplification and breast carcinogenesis. In this study we have examined the existence of a possible correlation between these genetic alterations in a panel of 83 malignant breast tumours (69 adeno and 14 lobular carcinomas). The status of a related gene, c-erbB3, was also examined. With the aid of microsattelite marker TP53CA loss of heterozygosity (LOH) was detected in the p53 locus in 49% of the tumours. Histochemical analysis of 64 of these tumours with the p53 antibody CM1 demonstrated staining, indicative of an elevated steady-state level of p53 protein in 23 rumours (36%). Amplification of the c-erbB2 gene was detected in 20 of 75 tumours analysed (27%). In the tumours with c-erbB2 amplification 12 also had p53 LOH. In at least another 2 tumours there was increased p53 protein level but no LOH. Therefore in 75% of the tumours with c-erbB2 amplification there was evidence of loss of normal p53 function. There was no evidence of c-erbB3 amplification in any of the 75 rumours analysed. The data presented demonstrates a strong correlation between the loss of p53 and tumour grade (p<0.00545), and a strong association between c-erbB2, but not c-erbB3, amplification and loss of p53 (p<0.0170).

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