Overview and new strategies in metastatic breast cancer (MBC) for treatment of tamoxifen-resistant patients.

The treatment with aromatase inhibitors (AIs) and fulvestrant has been demonstrated to be active in a proportion of tamoxifen-resistant breast cancer patients, obtaining, in some cases, a long-term control of tumor growth. Results from clinical trials indicate that treatment with fulvestrant might either precede or follow AIs. However, the AIs are now replacing tamoxifen as first-line advanced and adjuvant therapies, and thus, other options following tamoxifen failure are required. Fulvestrant may be effective in this setting, even if there is also evidence of a lack of cross-resistance between nonsteroidal and steroidal AIs, resulting in the potential use of steroidal AIs following nonsteroidal AI failure and vice versa. Resistance mechanisms to these therapies appear to be related to a cross talk between estrogen receptor (ER) and growth factor-signaling cascades. Novel therapeutic approaches for ER+ patients, which combine hormonal agents and signal transduction inhibitors, have been developed to overcoming resistance. Several trials are now investigating signal transduction inhibitors combined with endocrine agents. This approach might provide efficient treatments and delay the onset of antihormone resistance, thereby significantly improving patient's survival.