From the Sunnybrook Odette Cancer Centre, Department of Medicine, University of Toronto, Toronto, Ontario, Canada
Author's disclosure of potential conflicts of interest is found at the end of this article.
Address reprint requests to Kathleen I. Pritchard, MD, FRCPC, FACP, Professor, Sunnybrook Odette Cancer Centre, Department of Medicine, University of Toronto, 2075 Bayview Avenue, Toronto, ON M4N 3M5, Canada; e-mail: kathy.pritchard{at}sunnybrook.ca
Overview: Endocrine therapy remains a mainstay of treatment for women with breast cancer; therefore, it is important to have an understanding of the basic biology of endocrine sensitivity and resistance in breast cancer. Two-thirds of women and nearly 75% of postmenopausal women have positive estrogen receptors and/or progesterone receptors and are therefore candidates for adjuvant endocrine therapy. Potential approaches for such therapy include new classes of drugs, such as the selective estrogen receptor downregulators, of which the prototype is fulvestrant. There is interest in combining fulvestrant with an aromatase inhibitor based on promising preclinical data. Other endocrine combinations, innovative scheduling (i.e., intermittent use or alternating use of agents of different classes), optimizing the length of endocrine therapy, and combining new or targeted therapies may be important. Recent observations that have described host factors such as cytochrome P450 genotypes, which affect the metabolism and efficacy of endocrine agents, have provided new insight into optimal endocrine approaches and will require practical application.
