A 62-year-old woman was diagnosed with primary left breast cancer during a follow-up for an ovarian tumor. She had at first undergone surgical resection of an ovarian tumor, and a pathological examination had revealed ovarian cancer. Gynecologists decided to treat her ovarian cancer with chemotherapy, and we were initially planning to provide treatment for breast cancer after that was completed. Sentinel lymph node biopsy performed before chemotherapy revealed no axillary metastases. The patient received six courses of intravenous PTX (175 mg/m2 on day 1, every 3 weeks) and intravenous CBDCA (AUC6 on day 1, every 3 weeks) as combination therapy. Abdominal lymph node dissection was performed between chemotherapy courses 3 and 4. The lump in the left breast showed partial clinical response, and partial resection of the left breast was performed after completion of chemotherapy. In Japan, few cases of primary breast cancer treated preoperatively using carboplatin-containing regimens have been described.