5-Fluorouracil with leucovorin in breast cancer.

Extensive preclinical data have demonstrated that leucovorin can modulate 5-fluorouracil (5-FU) cytotoxicity. Additionally, randomized clinical trials have shown that leucovorin increases the therapeutic index of 5-FU in patients with advanced colorectal cancer, setting a new therapeutic standard for this disease. Based on this information, several controlled, but nonrandomized, clinical trials have examined the combination of 5-FU and leucovorin in patients with metastatic breast cancer. Although many of these trials are still ongoing, preliminary information suggests that leucovorin also potentiates 5-FU activity against breast carcinoma. However, to date, it has not been shown that leucovorin increases the therapeutic index of 5-FU in these patients. Continued testing of the role of leucovorin in combination chemotherapy for breast cancer appears warranted.