The aromatase inhibitors in early breast cancer: who, when and why?

The aromatase inhibitors deplete oestrogen by inhibiting aromatase, the enzyme that synthesises oestrogen from androgens. They are effective as therapies for breast cancer only in postmenopausal women whose tumours express oestrogen or progesterone receptors. As adjuvant therapy, tamoxifen and the aromatase inhibitors have similar efficacy in the first 5 years of treatment. Aromatase inhibitors can be used as an alternative to tamoxifen in women with symptomatic intolerance or a contraindication to tamoxifen. Early data suggest that switching to an aromatase inhibitor after 2-5 years of tamoxifen therapy is beneficial in women with high-risk disease. Aromatase inhibitors are associated with more hot flushes than placebo, but with fewer hot flushes, less endometrial toxicity and venous thromboembolism, and more arthralgia, myalgia and bone fracture than tamoxifen.