Estrogen Receptor Signaling in Breast Cancer

SIMPLE SUMMARY: Estrogens, belonging to a group of steroid compounds, play an important role in both physiological and disease processes, mainly by interacting with estrogen receptors (ERs). Abnormal ER signaling may result in various cancers, including breast cancer (BC), one of the most often diagnosed cancers in women globally, and a second cause of female cancer-related death. In the present review, we discuss the current knowledge of the estrogen receptor-dependent signaling pathways in breast cancer. The significance of clinical implications of ER signaling in BC, including the potential therapies, is also summarized. ABSTRACT: Estrogen receptor (ER) signaling is a critical regulator of cell proliferation, differentiation, and survival in breast cancer (BC) and other hormone-sensitive cancers. In this review, we explore the mechanism of ER-dependent downstream signaling in BC and the role of estrogens as growth factors necessary for cancer invasion and dissemination. The significance of the clinical implications of ER signaling in BC, including the potential of endocrine therapies that target estrogens’ synthesis and ER-dependent signal transmission, such as aromatase inhibitors or selective estrogen receptor modulators, is discussed. As a consequence, the challenges associated with the resistance to these therapies resulting from acquired ER mutations and potential strategies to overcome them are the critical point for the new treatment strategies’ development.