TY - JOUR T1 - Phase I Study of S-1 in Combination with Trastuzumab for HER2-positive Metastatic Breast Cancer JF - Anticancer Research JO - Anticancer Res SP - 3035 LP - 3039 VL - 31 IS - 9 AU - TAKAHIRO NAKAYAMA AU - SATOSHI MORITA AU - TSUTOMU TAKASHIMA AU - SHUNJI KAMIGAKI AU - KATSUHIDE YOSHIDOME AU - TOSHIKAZU ITO AU - TETSUYA TAGUCHI AU - JUNICHI SAKAMOTO AU - SHINZABURO NOGUCHI Y1 - 2011/09/01 UR - http://ar.iiarjournals.org/content/31/9/3035.abstract N2 - Background: As there are no reports of S-1 in combination with trastuzumab in clinical settings, we evaluated the safety and efficacy of S-1 in combination with trastuzumab for human epidermal-growth factor receptor (HER2)-positive metastatic breast cancer (MBC) and determined the recommended dose (RD). Patients and Methods: Patients with HER2-positive MBC received trastuzumab (a fixed initial dose of 4 mg/kg/day, then 2 mg/kg every week) plus S-1 (4 weeks followed by a 2-week rest) every 42 days. The dosage of S-1 was set of three levels (1: 80 mg/m2, 2: 65 mg/m2, 3: 50 mg/m2). The purposes of this study were the determination of the RD and safety. Dose-limiting toxicity (DLT) data were continually monitored to assess S-1 dose decreases. Results: Twelve patients were treated at level 1. Because no patients experienced DLT, the RD of S-1 plus trastuzumab therapy was 80 mg/m2 S-1 and 4 mg/kg followed by 2 mg/kg trastuzumab. The overall response rate and disease control rate were 33.3% and 83.3%, respectively. Conclusion: S-1 plus trastuzumab could be safely and effectively used for the treatment of HER2-positive MBC. The RD for a phase II study of this regimen was determined to be 80 mg/m2 S-1 and 2 mg/kg trastuzumab every week (loading dose, 4 mg/kg). ER -