ESR1 and breast cancer: For instance, PTEN an important negative regulator of the PI3K/AKT signaling pathways, which over activity leads to cell growth and tumor proliferation playing also an important role in endocrine resistance in breast cancer56, is involved in breast tumorigenesis and tumor progression and reduced expression of this gene in mammary tumor samples has been linked to a bigger tumors and higher pathological stages and the expression of estrogen receptor(ER) and the progesterone receptor (PR)57.