In the present report, we studied the ER-α36 function in ER-positive MCF-7 breast cancer cells and Hec1A endometrial cancer cells, and investigated the contribution of the MAPK/ERK and PI3K/Akt pathways mediated by ER-α36 to the agonist action of tamoxifen in endometrial cancer. Here, ESR1 is linked to breast cancer.