Safety issues surrounding the use of aromatase inhibitors in breast cancer

Third generation aromatase inhibitors (AIs) are now established therapy in advanced oestrogen receptor (ER)-positive breast cancer. As the use of AIs expands to include adjuvant treatment of early breast cancer and breast cancer prevention, tolerability and effects on other organs such as bone will become as important as the antitumour properties of the drugs. In direct comparisons with tamoxifen, AIs have a better toxicity profile with fewer patients stopping therapy because of drug-related side effects. There is a lower incidence of thromboembolic events and vaginal bleeding compared with tamoxifen. Although published information about the side effects of AIs is scarce, it is likely that they will have adverse effects on bone and possibly also on lipid metabolism. Subprotocols of ongoing adjuvant trials are investigating these effects. It is likely that the choice of which third generation AI to use will be largely determined by its tolerability and safety profile, since it is likely that the currently available drugs have similar efficacy.