Randomized phase II study of three doses of oral TAS‐108 in postmenopausal patients with metastatic breast cancer

This randomized phase II study was intended to identify the optimal dose of TAS‐108, a novel steroidal antiestrogen, for the treatment of breast cancer in postmenopausal Japanese women. The potential clinical effects of TAS‐108 on the uterus, bone, serum lipids, and hormones were also investigated. Postmenopausal women with hormone receptor‐positive metastatic breast cancer who had previously received one or two endocrine therapies were randomly assigned to one of the three possible dose levels of TAS‐108 (40, 80 or 120 mg/day). Oral TAS‐108 was given daily, and the efficacy and safety of the three doses were evaluated. A total of 97 patients (33, 32, and 32 in the 40‐, 80‐, and 120‐mg groups, respectively) were treated with TAS‐108. The clinical benefit rate was 30.3% for the 40‐mg, 25.0% for the 80‐mg, and 25.0% for the 120‐mg group. The 40‐mg group achieved the prespecified target threshold. TAS‐108 at all dose levels was well tolerated and appeared to have no harmful effects in terms of the variables examined in this study. We conclude that the optimal dose of TAS‐108 among the three doses is 40 mg, once daily, for further studies. JAPIC Clinical Trials Information number: Japic CTI – 121754.