A Preliminary Risk-Benefit Assessment of Paclitaxel

Paclitaxel is an antineoplastic agent, first isolated and described in 1971. Despite its novel structure and apparent activity in vitro, little interest was shown in developing the compound because of its scarcity, problems with its formulation and the mistaken assumption that its mechanism of action was similar to that of the vinca alkaloids. Approximately 10 years later, the unique mechanism of action of paclitaxel, its ability to stabilise microtubules, was discovered, and its activity against human tumour xenografts was demonstrated. Interest in the drug was reignited and clinical testing began. Severe hypersensitivity reactions were controlled in the phase II programme with a premedication regimen consisting of dexamethasone, histamine H₁-antagonists and H2-antagonists. Neutropenia was dose limiting in all studies conducted in patients with solid tumours. This toxicity was schedule-dependent, and less severe when paclitaxel was administered as a 3-hour infusion regimen. Peripheral neuropathy was mild to moderate in the initial experience, and dose-dependent. However, when bone marrow support with haemopoietic growth factors was used to allow paclitaxel dose intensification, neurotoxicity became dose limiting. To date, substantial clinical efficacy has been demonstrated in ovarian, breast, non-small-cell lung, and head and neck cancers. Response rates were low in initial studies in melanoma, prostate, colon, cervix and renal cancer. In December 1992, US Food and Drug Administration approval was granted for the use of paclitaxel as second-line therapy in ovarian cancer patients. More recently, similar approval was granted for use in recurrent breast cancer. Nevertheless, important questions remain. Such questions include: (a) the optimal dosage and schedule; (b) the use of paclitaxel as initial therapy; (c) its role in other malignancies; and (d) the development of suitable combination chemotherapy regimens.