[An early phase II clinical study of S-1 in patients with breast cancer. S-1 Cooperative Study Group (Breast Cancer Working Group)].

An early phase II clinical study of S-1 in patients with advanced or recurrent breast cancer was undertaken by a cooperative study group (Breast Cancer Working Group) of 14 institutes in Japan. S-1 was administered twice daily at 75 or 50 mg (dose FT)/body for 28 consecutive days with 14 days rest (one course). Twenty-eight patients were enrolled, 27 were eligible for the study, and 25 were evaluable for efficacy. Four complete responses and seven partial responses were obtained, and the response rate was 40.7% (11/27) [ninety percent confidence interval for this response was 26.7-56.4%]. The major adverse reactions observed were myelosuppression represented by leukopenia 44.4% (12/27), neutropenia 40.7% (11/27), RBC decreased 37.0% (10/27), hemoglobin decreased 29.6% (8/27), anorexia 55.6% (15/27), nausea/vomiting 48.1% (13/27), and fatigue 33.3% (13/27). The results suggested that the efficacy and safety of S-1 were effective against advanced or recurrent breast cancer. The objective of study judged should be investigated in a late phase II clinical study.