Fluorouracil-based combinations in the treatment of metastatic breast cancer

Although combination chemotherapy regimens may prolong survival for selected patients with metastatic breast cancer, few, if any, are cured. The standard regimens used in treatment, e.g., CMF (cyclophosphamide, methotrexate, and fluorouracil [5-FU]), FAC (5-FU, Adriamycin, and cyclophosphamide), and FEC (5-FU, epirubicin, and cyclophosphamide), were developed over a decade ago. Current efforts to improve therapeutic efficacy have concentrated on decreasing drug toxicity and increasing drug doses (e.g., high-dose chemotherapy with peripheral stem-cell support). An important alternative approach to increasing therapeutic efficacy focuses on altering the administration schedules of well-known chemotherapeutic agents and introducing active new agents. One of the most frequently used cytotoxic drugs, fluorouracil (5-FU), has documented activity in a variety of malignancies, most notably, breast cancer and gastrointestinal tract cancers. However, despite broad clinical experience with 5-FU, our knowledge about the mechanisms of resistance to the various administration schedules used is limited. In vitro data and clinical experience show that resistance to one schedule of 5-FU can be overcome by using alternative schedules, in particular, a protracted infusion. This article discusses our clinical experience with weekly high-dose 24-hour infusions of 5-FU in combination with folinic acid (leucovorin) alone and together with paclitaxel (Taxol) for the treatment of advanced breast cancer.