The main purpose of this study is to determine if taking the study drug, conjugated estrogens/bazedoxifene (Duavee®) causes any changes in the proliferation markers within the breast tissue of the study subjects. The study drug is approved by the US Food and Drug Administration in healthy postmenopausal women to treat certain symptoms of menopause such as hot flashes. Since it is not approved in women with DCIS, its use in this study is experimental. This study will also look at whether taking the study drug causes any significant or undesirable side effects in women with DCIS. The researchers hope that this study will help them determine if taking the study drug is safe in women taking DCIS and if it can possibly reduce the risk of developing breast cancer in women with DCIS.