The NEOLETEXE trial: a neoadjuvant cross-over study exploring the lack of cross resistance between aromatase inhibitors.

The aromatase inhibitor letrozole (Femar/Femara) and the aromatase inactivator exemestane (Aromasin) differ in their biochemical effect on the aromatase enzyme. Letrozole is a competitive aromatase inhibitor while exemestane binds irreversibly to the aromatase enzyme. This pharmacological difference is of clinical interest since a lack of cross-resistance has been documented.