165 Background: Advanced breast cancer can respond to S-1. Other oral fluoropyrimidine-based regimen, tegafur-uracil (UFT) was proven to be effective as adjuvant chemotherapy in Japanese breast cancer patients. Adjuvant chemotherapy with S-1 was useful in gastric cancer patients and S-1 with concurrent radiotherapy was safe and effective in several kinds of cancer patients. We tested S-1 and concurrent radiotherapy as adjuvant therapy in curatively resected breast cancer patients after standard primary systemic chemotherapy. Methods: Adjuvant chemotherapy with S-1 consisted of eighteen courses (2-week administration and 1-week withdrawal), at 80-120 mg/body per day. In cases judged to require postoperative radiotherapy, it was concurrently initiated on day1 of the study (a fractional daily dose of 1.8 Gy, up to a total dose of 50.4Gy). If estrogen receptor and/or human epidermal growth factor receptor 2 were positive, endocrine therapy and/or trastuzumab were permitted concurrently. Results: Among 45 patients enrolled between September 2007 and September 2009 from 3 institutions, 43 patients were eligible. 32 patients (74.4%) received concurrent radiotherapy. 22 patients (51.2%) completed the scheduled courses of chemotherapy. The most common reason for withdrawal of treatment was the request to discontinue in 8 patients (38.1%) between 6 courses of the beginning due to subjective symptoms, such as anorexia. It was followed by the detection of recurrence in 7 patients (33.3%). Among 36 patients without recurrence, the planned courses of S-1 were administered to 22 patients (61.1%), and the cumulative rates of administration for 365 days were 66.4% (95%CI: 50.8-79.1%). Although grade 3 neutropenia (8.9%), leukopenia (4.4%), and diarrhea (4.4%) were observed, they were manageable, and no grade 4 adverse effects appeared. Conclusions: Except for a relative many withdrawal of treatment due to subjective symptoms in early courses, adjuvant chemotherapy with S-1 and concurrent radiotherapy have an acceptable toxicity profile, and it seems feasible. A phase III trial investigating the usefulness of adjuvant S-1 is now ongoing in Japan.
Safety and feasibility of adjuvant chemotherapy with S-1 in Japanese breast cancer patients after primary systemic chemotherapy: a feasibility study