In the early stages of breast cancer, an important component of cell transformation are epigenetic changes in the genes encoding proteins that are involved in the regulation of cell proliferation and differentiation . For proteins that perform the role are nuclear receptors : estrogen ? (ER ? ) And retinoic acid ? 2 ( RAR 2 ) . On the basis of genetic testing breast cancer cells susceptible to the action of preparations insensitive przeciwestrogennych and retinoic acid derivatives , it was found that the cell resistance to drugs of this type may overflow into you with restrained expression at the transcriptional level , these receptor genes . Silencing gene expression of ER ? and RAR ? 2 is often associated with changes ( hypermethylation ) pattern of methylation of promoter regions of these genes. These changes are an essential part of the complex process of inactivation of chromatin that accompanies malignant transformation of cells. Evaluation of changes in the pattern of methylation of promoter regions of genes ER ? and RAR ? 2 and evaluation of the possibility of reactivating genes should have important pharmacological importance for the selection of an effective combination therapy to inhibit breast cancer cell proliferation .