47PInvestigation of the use of a novel S-1 administration method for treating metastatic and recurrent breast cancer

Abstract Background When considering treatment for metastatic and recurrent breast cancer, it is necessary to select drugs with emphasis on side effects and QOL. In Japan, oral 5-FU drugs have often been used for initial treatment. In the conventional schedule of S-1 for 4-week administration period followed by 2-week rest, the inferiority of S-1 to T has already been proved. In this study, we examined the efficacy and safety of the schedule of S-1 for 2-week administration period followed by 1-week rest, which is considered to have less side effects and better compliance. Methods We enrolled individuals with HER2-negative breast cancer who had not received chemotherapy after diagnosis of metastatic breast cancer. S-1 (40-60 mg, twice daily) was administered consecutively for 14 days followed by 7 days of rest (1 course). The primary endpoint was progression-free survival (PFS); the secondary endpoints were overall survival (OS), time to treatment failure (TTF), response rate (RR), disease control rate (DCR), and adverse events. Results Between September 1, 2013 and August 31, 2016, 32 patients were enrolled. Median PFS was 7.8 months (1.4-35.4 months), and median OS was 25.2 months (4.8-47.8 months). TTF was 9.1 months. RR was 31.3%, and the DCR was 78%. The cumulative rates of the relative total administration dose of S-1 was 95.6%. Incidence of grade 3 side effects were neutropenia (9.4%), leukopenia (3.1%), anorexia (3.1%), ocular symptoms (3.1%), and an increase in total bilirubin levels (3.1%). Conclusions The schedule of 2-week administration period followed by 1-week rest seems to be safe and effective for primary treatment of metastatic and recurrent breast cancer. Legal entity responsible for the study Kobe Breast Cancer Oncology Group. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.