Expression of DNA methylation-related proteins in metastatic breast cancer

We aimed to investigate the expression of methylation-related proteins (5-meC and DNMT1) in the metastatic breast cancers of variable sites and its association with clinicopathologic factors. A total of 126 metastatic breast cancers (31 bone metastases, 36 brain metastases, 11 liver metastases, 48 lung metastases) were made into tissue microarray and immunohistochemical staining of ER, PR, HER-2, Ki-67, 5-meC, and DNMT1 were performed. Molecular classification was made on the basis of immunohistochemical staining result of ER, PR, HER-2, Ki-67; luminal A, luminal B, HER-2, triple negative breast cancer (TNBC). Methylation-related proteins were differentially expressed based on the metastatic sites. Tumoral and stromal 5-meC showed the lowest expression in the bone metastasis (P < 0.001), tumoral DNMT1 showed the least expression in bone metastasis and the highest expression in the brain metastasis (P < 0.001). Expression of DNMT1 was correlated with ER negativity (P = 0.004), PR negativity (P = 0.011), HER-2 positivity (P = 0.016), higher Ki-67 labeling indices (P = 0.016), and non-luminal A type (P = 0.017). DNMT1 positivity was associated with shorter overall survival in bone metastasis (P = 0.017) and lung metastasis (P = 0.028) by univariate analysis. In conclusion, methylation-related proteins differentially expressed according to the metastatic sites in metastatic breast cancer. Tumoral and stromal 5-meC showed the lowest expression in the bone metastasis. Tumoral DNMT1 expression was low in bone metastasis and highest in brain metastasis.