[A patient with of metastatic breast cancer with a well-controlled quality of life using S-1 therapy as first-line chemotherapy].

We experienced a case of endocrine therapy-resistant recurrent breast cancer with liver and bone metastases, treated with S-1 as first-line chemotherapy and maintaining a good quality of life. The patient was a 31-year-old premenopausal woman. She was diagnosed with cancer of the left breast(T1(18mm), N0, M(-))and underwent breast-conserving surgery, sentinel lymph node biopsy, and radiation therapy in August 2002. As there was hormone sensitivity, she was treated with LHRH analog for 3 years and tamoxifen for 5 years as adjuvant therapy. After her first childbirth, she had a recurrence of liver and bone metastases. After treatment with endocrine therapy failed, an oral administration of S-1 was initiated as first-line chemotherapy considering her QOL. She received 8 months of S-1 therapy with no severe adverse reactions and maintained a high quality of life. Treatment with S-1 is thought to be useful for first-line chemotherapy if the treatment demonstrates a therapeutic equivalence with taxane on patients' overall survival.