Cross-resistance to different aromatase inhibitors in breast cancer treatment

Recent studies have documented the biochemical and clinical efficacy of nov el aromatase inhibitors. These drugs belong to one of two classes: non-ster oidal and steroidal drugs, known to be different with respect to enzyme bin ding site and their effect on the aromatase enzyme. Several studies have no w confirmed a lack of complete cross-resistance to drugs of the two classes . While some of these observations may be explained by a more potent aromat ase inhibition caused by some aormatase inhibitors compared to others, this is not always the case. Such observations therefore focus on the importanc e of alternative mechanism of action like a differential influence on the i ntratumour aromatase enzyme by the different drugs. Current and future stud ies should aim at exploring the mechanism of cross-resistance and evaluate optimal use of different aromatase inhibitors in sequence or probably, also in concert.