Emerging agents in the treatment of anthracycline- and taxane-refractory metastatic breast cancer.

Despite the recent trend toward treatment of early stage breast cancer aggressively with anthracyclines and taxanes, nearly half of those women will have metastatic recurrence. Moreover, because of the increasing prior exposure to these drugs, far more women facing first-line therapy for recurrent disease will now have developed anthracycline- and taxane-refractory metastatic breast cancer (ATRMBC), presenting a major therapeutic challenge. A number of established drugs are showing promise in this setting: capecitabine alone or combined with lapatinib; gemcitabine; vinorelbine; and oxaliplatin. At the same time, a variety of new drugs are emerging for potential use in ATRMBC. Among the drugs in clinical development that have shown promising activity include novel classes of compounds (camptothecins and epothilones), newer members of established classes (pemetrexed and vinflunine), and agents with novel mechanisms of action (the mitosis inhibitor E7389 and the ascidian-derived anticancer compound trabectedin). Several molecularly targeted agents are also being evaluated in ATRMBC, including interleukin-2 receptor-binding denileukin diftitox, and 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), which inhibits the protein chaperone heat shock protein 90.