70% of breast cancers are estrogen receptor α (ERα)-positive. ERα is the antenna that senses the ovarian hormone estrogen (E2) and drives tumour cell proliferation and spreading. 4OH-tamoxifen and faslodex are given to patients to prevent cancer growth and spreading but they possess serious side effects. Thus, additional drugs are needed to fight breast cancer. We will explore existing drugs for the possibility of ‘reuse’ as breast cancer drugs.