Phase II Study to Evaluate Tariquidar (XR9576), a Selective MDR-1 Inhibitor, in Chemotherapy Resistant Advanced Breast Cancer

The primary objective of this phase II study is to assess if XR9576, a selective MDR-1 inhibitor, is able to reverse primary doxorubicin or taxane resistance in advanced breast cancer. Clinical activity will be measured by objective tumor response rates observed after treatment with XR9576 in combination with taxane or anthracycline containing chemotherapy in patients previously resistant to the same agent(s).

The secondary objectives of the study are to assess the biological activity of XR9576 and evaluate MDR-1 expression in these tumors. The MDR-1 inhibitory activity of XR9576 will be evaluated by serial sestamibi scans of the tumor. MDR-1 expression will be detected by immunohistochemistry.