[CGS20267 (Letrozole), a new aromatase inhibitor: late phase II study for postmenopausal women with advanced or recurrent breast cancer (no. 1)--investigation of recommended clinical dose CGS20267 Study Group].

To determine the recommended clinical dose of CGS20267 (Letrozole), we conducted a randomized comparative study as a late phase II study (first part) in postmenopausal women with advanced or recurrent breast cancer. Forty-one patients were randomly assigned to receive 0.5 mg or 1.0 mg once daily. There were no statistically significant differences in background between the two groups. Although there was no significant difference in the objective response rates between the two groups, the rate was higher at 1.0 mg (44.4%) than at 0.5 mg (38.1%). We also combined these data with the results of an early phase II study. The objective response rates (CR + PR) were 31.4% at 0.5 mg and 42.2% at 1.0 mg, and response rates consisting of CR, PR, and NC for longer than 6 months were significantly higher at a dose of 1.0 mg (68.9%) than 0.5 mg (41.2%). Side effects included drug-related adverse events in 36.8% at 0.5 mg and in 31.6% at 1.0 mg. All of the events were grade 2 or lower, indicating a favorable tolerability of CGS20267. These results demonstrated that CGS20267 1.0 mg once daily is more effective than 0.5 mg, and has comparable safety, in the treatment of postmenopausal women with advanced or recurrent breast cancer. We conclude the recommended clinical dose of CGS20267 should be 1.0 mg once daily.

[CGS20267 (Letrozole), a new aromatase inhibitor: late phase II study in postmenopausal women with advanced or recurrent breast cancer (no. 2)--evaluation of efficacy and safety at the recommended clinical dose CGS20267 Study Group].

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.

[CGS 20267 (Letrozole), a new aromatase inhibitor: early phase II study for postmenopausal women with advanced breast cancer].

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.