Recent studies have documented the biochemical and clinical efficacy of novel aromatase inhibitors. These drugs belong to one of two classes: non-steroidal and steroidal drugs, known to be diffeent with respect to enzyme binding site and their effect on the aromatase enzyme. Several studies have now 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 aromatase inhibition caused by some aormatase inhibitors

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... compared to others, this is not always the case. Such observations therefore focus on the importance of alternative mechanism of action like a differential influence on the intratumour aromatase enzyme by the different drugs. Current and future studies should aim at exploring the mechanism of cross-resistance and evaluate optimal use of different aromatase inhibitors in sequence Endocrine-Related Cancer (1999) 6 251-257 or probably, also in concert.