Approximately 75% of breast cancers express the estrogen and/or progesterone receptor (hormone receptors). The standard of care for women with hormone receptor positive breast cancer is five to ten years of adjuvant endocrine therapy with drugs such as tamoxifen or aromatase inhibitors (AIs). In women with stage I-III breast cancer, treatment with adjuvant endocrine therapy has been shown to reduce recurrences by 30-50% and improve survival. Unfortunately, it is estimated from large population databases that up to 35-40% of patients may discontinue adjuvant endocrine therapy before completing the recommended 5 years for various reasons, and non-adherence may reduce survival.