[Methylation and expression of gene p16INK4a and RB in breast carcinoma]

(1) To investigate the promoter methylation status of gene p16(INK4a) and gene RB in breast carcinoma and the adjacent non-neoplastic hyperplastic epithelial tissue. (2) To study the correlation of p16(INK4a) gene expression at protein level with the abnormal gene methylation, the clinical manifestation and the pathological parameters.

Methylation status of promoters of p16(INK4a) gene and RB gene was detected by using methylation specific PCR in 46 cases of breast cancer, 22 cases of the adjacent non-neoplastic hyperplastic epithelium tissue and 7 cases of normal breast tissue. In addition, the p16(INK4a) gene protein expression level was also detected using immunohistochemical technique(SP method) in 46 cases of breast cancer and 22 cases of the adjacent hyperplastic epithelial tissue.

The methylation rate of p16(INK4a) gene was 23.9% (11/46) in breast cancer, 18.2% (4/22) in the adjacent non-neoplastic hyperplastic epithelial tissue and 1/7 in normal breast tissue, respectively. The methylation rate of RB gene was relatively low, which was 10.8% (5/46), 9.1% (2/22) and 0(0/7) in the above 3 groups, respectively. Methylation rate of p16(INK4a) gene and RB gene was not significantly different among the breast cancer, the adjacent non-neoplastic hyperplastic tissue and the normal tissues (P > 0.05). However, the methylation status of p16(INK4a) gene was closely correlated with its protein expression level and the negative ER expression result of the breast cancer (P < 0.05), but not correlated with the size of the cancer, differentiation status, lymph node metastasis, and age. The methylation status of RB gene was correlated with lymph node metastasis, but not with the size, the differentiation status, ER expression of the breast cancer and the age of the patients.

The abnormal methylation of p16(INK4a) gene may not play a significant role in the early stage of breast cancinogenesis, but may play a role of in the progression of the cancer. RB gene methylation may also be a indicator in choice to identify the progression and prognosis of breast cancer.