Nab-paclitaxel for breast cancer: a new formulation with an improved safety profile and greater efficacy

Taxanes, paclitaxel and docetaxel, are among the most effective agents used to treat breast cancer. Nab-paclitaxel (ABI-007, Abraxane®) is paclitaxel encapsulated in albumin. This differs from the more conventional formulation which uses cremophor to increase the solubility of paclitaxel (CrEL-paclitaxel). In a randomized trial that formed the basis of its regulatory approval in the USA, 3-weekly nab-paclitaxel induced a higher response rate and longer time to progression than CrEL-paclitaxel in patients with metastatic breast cancer. Except for grade 3 sensory neuropathy, nab-paclitaxel was also safer. An interim analysis from a more recent randomized Phase II trial suggests that weekly nab-paclitaxel is more effective and safer than either 3-weekly nab-paclitaxel or 3-weekly docetaxel. The superior efficacy of nab-paclitaxel is presumably due to the improved safety profile, which allows for the administration of higher doses, a greater proportion of which actually reaches the tumor. Observations on the development of nab-paclitaxel have important implications for our understanding of dose response in the use of cytotoxic drugs to treat all forms of cancer. Although it is not yet clear whether nab-paclitaxel can be routinely substituted for CrEL-paclitaxel or docetaxel in breast cancer treatment regimens, it seems highly likely that this will occur within the next 5 years.