Why are aromatase inhibitors superior to tamoxifen?
Superficially, one would expect little difference between the two treatment types because both effectively reduce oestrogenic stimulation of breast cancer cells. However, there are clearly major differences in the mechanisms of action of the two treatments. Greater response rates indicate that there are a group of tumours that respond to AIs but not to tamoxifen. Increased time to progression using AIs suggests that resistance to tamoxifen arises sooner than does resistance to AIs. Unravelling the mechanisms responsible for the superiority of AIs is not only of interest biologically but it may also be help to achieve further improvements in endocrine therapy in the future. Neoadjuvant trials are most helpful with respect to investigating the mechanism responsible for the difference in effectivess between the two types of treatment because tissue before, during and immediately after treatment is available and can be assayed for potential markers of increased response using a variety of
