The tumour suppressor protein PTEN (also called MMAC1 and TEP1) is a dual specificity phosphatase, recognizing both lipid and protein substrates. By its lipid phosphatase activity, PTEN dephosphorylates phosphatidylinositol 3,4,5-triphosphate (PIP-3), which leads to negative regulation of serine-threonine kinase Akt (PKB). By its protein phosphatase activity, PTEN participates in regula- tion of MAP kinase signalling pathway through dephosphorylation of FAK and Shc proteins.

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 ) .