Aromatase inhibitors for breast cancer: Lessons from the laboratory

Endocrine therapy with tamoxifen has been the mainstay of treatment for hormone-sensitive breast cancer for more than 20 years. An alternative strategy of oestrogen deprivation in postmenopausal women with aromatase inhibitors is set to replace tamoxifen based on better efficacy and a delay in the emergence of endocrine resistance. There are fundamental differences in how tamoxifen and aromatase inhibitors alter oestrogen-receptor signalling. Understanding the response and resistance to these different therapies is central to further improving therapeutic options for women with breast cancer.