Paclitaxel in Breast Cancer

Paclitaxel has emerged as an important agent in the treatment of breast cancer. The efficacy and tolerability of this agent, as well as its lack of cross-resistance with anthracyclines, have spurred intensive clinical investigation worldwide. Optimization of paclitaxel dose and scheduling and evaluation of the drug in combination regimens are a central focus of investigations. Recent clinical evidence suggests that optimal dose of single-agent paclitaxel by 3-h infusion is 175 mg/m². Trials evaluating administration schedule have not found either a 24-h or 96-h infusion to be superior to a 3-h infusion. Weekly moderate-dose paclitaxel administration is also generating much interest, given the high relative dose intensity and dose density delivered, yet very modest myelosuppression and manageable neurotoxicity observed. As first-line therapy in metastatic disease, multiple studies have documented overall response rates in the range of 30%-60%. As second-line or salvage single-agent therapy in metastatic patients, paclitaxel generally affords an overall response rate of 20%-40%, even in anthracycline-resistant patients. The novel mechanism of action and manageable toxicity of paclitaxel has led to successful incorporation into combination chemotherapy regimens. The combination of paclitaxel and doxorubicin has been the most extensively studied, with the role of this regimen continuing to evolve. Other combination regimens that appear to hold substantial promise as first-line metastatic treatment are paclitaxel with carboplatin and paclitaxel with trastuzumab (anti-HER2 antibody). The favorable results obtained in the metastatic setting have prompted phase II and phase III investigations of paclitaxel in the adjuvant and neoadjuvant settings. In the adjuvant setting, a recent phase III study has indicated that the addition of sequential paclitaxel to standard therapy affords both disease-free and overall survival benefits. Current investigations with paclitaxel will continue to optimize the role of this agent in the treatment of early- and advanced-stage breast cancer, addressing not only response rates but also survival and quality-of-life issues. The use of paclitaxel on a weekly schedule or with new therapeutic modalities, such as monoclonal antibodies, is also receiving much attention. While it is clear that paclitaxel is a very active agent in the treatment of breast cancer, it is hoped that these innovative trials will further maximize the potential of this agent in patients with breast cancer.