A Qualitative Systematic Review of the Evidence Base for Non-cross-resistance between Steroidal and Non-steroidal Aromatase Inhibitors in Metastatic Breast Cancer

This review suggests that switching from an NSAI to an SAI is a reasonable option. This would be particularly important for patients who would probably respond to further endocrine manoeuvres; strongly oestrogen receptor-positive disease, non-visceral disease, a good prior response or a long duration of response. Further research to optimise the sequence of endocrine therapies in metastatic breast cancer is needed.