[A patient with pulmonary metastasis from breast cancer after surgery who responded to S-1].

We report a 60-year-old female with pulmonary metastasis from breast cancer who responded to S-1. In November 2001, she underwent surgery. In October 2005, relapse was detected. As there was no hormone sensitivity, chemotherapy was selected, and oral administration of S-1 at 120 mg/day (2 divided doses) was initiated. After the fourth course, the tumor marker level returned to the reference value. Thoracic CT at the end of the sixth course revealed the disappearance of the metastatic focus. Adverse reactions during the administration period were mild. S-1 showed potent antitumor effects and good tolerance, and it may be useful for treating metastatic/recurrent breast cancer.