Furthermore, tamoxifen effects on endometrial receptivity have not been investigated yet. Although to date no single, clinically relevant morphologic, molecular, or histologic marker capable of indicating endometrial receptivity status has been identified. Few genes were found to be associated with implantation and could act as potential markers for receptivity and can be used to compare endometrial receptivity in patients previously treated with Tamoxifen to normal population. The research will use several genes that have been proven to have high correlation with implantation process and endometrial receptivity.