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.