A multicenter, open labeled, randomized early Phase II study for CGS 20267 was conducted at the doses 0.5 mg once daily and 1.0 mg once daily in postmenopausal women with advanced breast cancer. Sixty-four patients were randomly assigned to the doses of either 0.5 mg once daily (n = 33) or 1.0 mg once daily (n = 31). Thirty-one patients were eligible for 0.5 mg group, and 29 for 1.0 mg group. A total of 57 patients (30 in the 0.5 mg group and 27 in the 1.0 mg group) were eligible for the evaluation of efficacy. There were 3 CR, 5 PR, 5 stable disease (SD: NC lasting over 24 weeks), 7 NC and 10 PD in the 0.5 mg group. The objective response rate (ORR) was 26.7%. There were 4 CR, 7 PR, 8 SD, 3 NC and 5 PD in the 1.0 mg group. The ORR was 40.7%. A total of 57 patients (29 in the 0.5 mg group and 28 in the 1.0 mg group) were eligible for safety evaluation. Adverse clinical events related to CGS 20267 in the 0.5 mg group were headache, nausea, cold sweat, sleepiness and muscle ache in the lower extremities (2 patients, incidence rate 6.9%) whereas those in the 1.0 mg group were generalized itching and generalized hot feeling (2 patients, incidence rate 7.1%). All of the adverse events were grade 1 except the generalized itching which was grade 2. CGS 20267-related abnormalities in the laboratory tests for the 0.5 mg group were a decrease in WBC, and increases in GOT, GPT, LDH and gamma-GTP (5 patients, 14.3%) whereas those in the 1.0 mg group were increases in GPT, gamma-GTP, alkaline phosphatase, and total bilirubin (1 patient, 3.6%). The increases in GOT and GPT were grade 2, but others were grade 1. The data show both CGS 20267 0.5 mg once daily and 1.0 mg once daily to be effective and tolerable in the treatment of postmenopausal women with advanced breast cancer.