Investigation of a Novel S-1 Administration Schedule for Treating Metastatic and Recurrent Breast Cancer (KBCOG13).

Background/aim S-1, a 5-fluorouracil(5-FU) oral anti-cancer drug, has been traditionally used with a schedule of 4-week oral administration followed by 2-week rest for breast cancer treatment. We, herein, aimed to investigate the clinical efficacy and safety of a schedule of 2-week oral administration followed by 1-week rest for patients with metastatic breast cancer. Patients and methods We enrolled patients with HER2-negative metastatic breast cancer who had not received prior chemotherapy. S-1 was administered consecutively for 2-weeks followed by a 1-week rest. Results Between September 1, 2013 and August 31, 2016, 32 patients were enrolled. The median follow-up time was 32.1 months. The median progression-free survival (PFS) was 9.4 months. Overall survival (OS) was 41.0 months, time to treatment failure (TTF) was 7.8 months, response rate (RR) was 31.3%, and disease control rate (DCR) was 78.1%. The incidence of grade 3 side-effects was not high. Conclusion The 3-week schedule of S-1 can be considered useful as a treatment for patients with metastatic breast cancer, helping in maintaining a high quality of life.