Most breast cancers require estrogen to grow. These are treatable and often curable with anti-estrogen therapies, but for some women the breast cancer will come back, sometime many years later. When breast cancers recur, they are often resistant to the treatment that the patient initially received. The standard therapy then is a combination treatment that works well for many, but not all women. Dr. Horwitz in collaboration with Dr. Carol Sartorius is conducting studies to test an alternative and less toxic approach for women with recurrent estrogen-drive breast cancers.