Although many improvements in prognostic and therapeutic treatments for Breast Cancer(BC) have been made, metastasis remains the major cause of all BC related deaths. Hormonal estrogen plays a crucial role in the maintenance of bones and BC formation. Its cellular mechanism of action is mediated by the nuclear receptor Estrogen receptor-1 (ERα) where status of primary tumor estrogen responsiveness (positive or negative) is used as a prognostic indicator in the treatment of BC and correlates with ER status of bone metastasis. Patients with ER+ BC develop bone metastasis three times more than patients negative for ER. Previous research shows that stable introduction of ERα in ERα negative BC cells can inhibit their skeletal metastasis in mice models. This project assess whether ERα positive cells migrates preferentially towards bone cells in presence of bone marrow derived cells in vitro.