In the first part of this late phase II study, we determined the recommended clinical dose of CGS20267 to be 1.0 mg once daily for the treatment of postmenopausal women with advanced or recurrent breast cancer. To further evaluate the efficacy and safety of CGS20267 at the derived or recommended clinical dose, 30 more patients were enrolled in the second part of the study, and were added to the patients treated at 1.0 mg in the first part. As a result of putting the first and second parts together, the objective response rate at 1.0 mg was found to be 38.3%, which was almost equal to that of the early phase II study (40.7%). Drug-related adverse events occurred in 35.4% of the patients at 1.0 mg, and all of the events were of grade 2 or lower. These results demonstrated that CGS20267 1.0 mg once daily is effective and well tolerated in the treatment of postmenopausal women with advanced or recurrent breast cancer.