Adjuvant Systemic Therapy: Endocrine Therapy

Abstract

Estrogen receptor (ER)-positive and/or progesterone receptor (PR)-positive breast cancers are the most common types of breast cancer, accounting for 75% of all breast cancers. Adjuvant endocrine therapy is a pivotal component of treatment for women with hormone receptor-positive early-stage breast cancer; it delays local and distant relapse and prolongs survival. Patients with ER- and/or PR-positive invasive breast cancers should be considered for adjuvant endocrine therapy regardless of age, lymph node status, or adjuvant chemotherapy use. Features indicative of uncertain endocrine responsiveness include low levels of hormone receptor immunoreactivity, PR negativity, poor differentiation (grade 3), high Ki-67 index, human epidermal growth factor receptor 2 overexpression, and high gene recurrence score. Adjuvant hormonal manipulation is achieved by blocking the ER in breast tumor tissues with tamoxifen in premenopausal and postmenopausal women, lowering systemic estrogen levels with luteinizing hormone-releasing hormone agonists in premenopausal women, or blocking estrogen biosynthesis in nonovarian tissues with aromatase inhibitors in postmenopausal women.