Oral 5-FU analogues in the treatment of breast cancer

Three oral 5-fluorouracil (5-FU) therapies have been approved by the US Food and Drug Administration or are in development for the treatment of patients with breast cancer: capecitabine, UFT, and 5-FU/eniluracil. Capecitabine has been approved for breast cancer patients whose disease is paclitaxel-resistant, and either anthracycline-resistant or for whom further anthracycline use is not indicated. A response rate of 20% was observed in an open-label phase II trial of capecitabine in heavily pretreated patients with metastatic breast cancer. Diarrhea and hand-foot syndrome were the most frequently reported toxicities. In a randomized phase II study of capecitabine vs paclitaxel in breast cancer patients who had failed anthracyclines, response rates were 36% for capecitabine vs 21% for paclitaxel. Several phase II trials of 5-FU/eniluracil in breast cancer are ongoing. Preliminary response data from one of these trials on 31 patients with anthracycline- and taxane-resistant advanced breast cancer showed a 16% partial response rate. Grade 3-4 treatment-related toxicities included diarrhea (8%), nausea (3%), and granulocytopenia (3%). In Japan, UFT is widely used for the treatment of breast cancer in both the adjuvant and metastatic settings, though studies in the United States are just getting under way. A phase II trial conducted in Madrid, Spain evaluated the combination of UFT, methotrexate, and leucovorin as salvage therapy for breast cancer patients. The overall response rate was 38% among 21 patients, and diarrhea was the most common toxicity. Many questions remain unanswered about the optimal use of oral 5-FU agents in breast cancer. There seems little question that these agents have substantial activity and will find a place in the therapeutic armamentarium.