In metastatic breast cancer (MBC) patients who have already received anthracyclines, taxanes, antimetabolites and vinca-alkaloids and have developed drug resistance to these drugs, therapeutic options are very limited. Alkylating agents showed a modest activity in pretreated metastatic breast cancer. This phase III trial will compare the effectiveness and the safety profile of vinflunine to an alkylating agent of physician choice in MBC patients who have exhausted anthracyclines, taxanes, antimetabolites and vinca-alkaloids.