A phase II study of 17-allylamino-17-demethoxygeldanamycin in metastatic or locally advanced, unresectable breast cancer.

Heat shock protein 90 (Hsp90) is an attractive target for breast cancer treatment, as it is required for the proper folding and stabilization of several proteins known to be involved in breast cancer growth and development. These proteins include the epidermal growth factor receptor, human epidermal growth factor receptor 2 (HER2), estrogen receptor (ER), progesterone receptor (PR), and src. 17-Allylamino-17-demethoxygeldanamycin (17-AAG) is an intravenous Hsp90 inhibitor in development for breast cancer treatment. We conducted a phase II study of 17-AAG 220 mg/m(2) on days 1, 4, 8, and 11 every 21 days in patients with metastatic and locally advanced breast cancer. Since we expected the molecular effects of Hsp90 inhibition to extend beyond just ER, PR, and HER2 down regulation and to impact a variety of other cellular proteins, patients were not selected based on ER, PR, or HER2 status. Eleven patients, including 6 patients with triple negative breast cancer, were enrolled and treated. There were no responses and 3 patients had stable disease as their best response. Five patients developed grade 3/4 toxicities, which were primarily hepatic and pulmonary. Based on these results, we do not recommend further study of 17-AAG at this dosing schedule or in unselected breast cancer patients.