Paclitaxel combination therapy in the treatment of metastatic breast cancer: a review.

Combinations of active antineoplastic agents have been the most effective treatment for metastatic breast cancer. Criteria for an effective combination include use of drugs with different mechanisms of action, nonoverlapping toxic effects, and synergistic, or at least additive, antitumor activity. Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ), with its unique mechanism of action, offers an excellent opportunity for development of effective combination therapy against breast cancer. However, a number of problems have hindered the rapid development of effective combinations. The most obvious problem is the lack of a defined optimal dose and schedule of administration. The second problem has been the demonstration of unexpected interactions between paclitaxel and the other component(s) of the combination, often resulting in unusual and serious toxic effects. This review will focus on the phase I and II trials of paclitaxel in combination with established antineoplastic drugs (except doxorubicin and congeners, which is covered elsewhere in this issue) for breast cancer: cisplatin, 5-fluorouracil with or without folinic acid, cyclophosphamide, radiation therapy, as well as novel investigational agents or strategies, edatrexate, monoclonal antibodies to oncogenes, growth factors, and gene therapy with insertion of multidrug resistance gene into blood stem cells. Combination therapy offers exciting possibilities of enhanced antitumor efficacy. However, given the unexpected and serious toxic effects observed, only proven combinations should be used outside the context of a clinical trial. Additionally, the burden of proof will be to show that these combinations have increased antitumor activity, decreased toxicity, or both compared with single-agent paclitaxel.