Methylation in the p53 promoter is a supplementary route to breast carcinogenesis: correlation between CpG methylation in the p53 promoter and the mutation of the p53 gene in the progression from ductal carcinoma in situ to invasive ductal carcinoma.

Aberrant methylation in the CpG sites located in the promoter region of several tumor suppressor genes has been reported in various types of cancers. However, the methylation status of the p53 promoter has not been clearly determined and no information is available on its role in breast cancer. The aim of the study was to determine the presence and timing of the methylation of CpG sites in the p53 promoter, in the progression from ductal carcinoma in situ to invasive cancer. We also explored the correlation between the CpG methylation of the p53 promoter and p53 mutation during the progression of breast cancer. The corresponding lesions of both the invasive and noninvasive types were microdissected in paraffin-embedded tissue of 26 breast carcinomas. Bisulfite-modified DNA sequencing for methylation status in the p53 promoter was carried out, and double-strand DNA sequencing was performed in the promoter region and exons 4 to 9 of the p53 gene. CpG site methylation in the p53 promoter was detected in three cases (11.5%). Two noninvasive and three invasive lesions harbored CpG methylation in the p53 promoter. Methylations in more than one site were observed in three lesions, all of which contained methylation in two sites. The methylated CpG sites were located near the AP1 and YY-1 binding sites and at the YY-1 binding site. The p53 mutation was not found in the lesions where methylation in p53 promoter region was evident. In 16 cases (61.5%), neither methylation nor p53 mutation was detected. We conclude that the methylation in the p53 promoter region is found in the breast cancer irrespective of the status of invasion, and that the hypermethylation in the p53 promoter region is an alternative pathway to tumorigenesis where there is no p53 gene mutation.