 This is a national, multicenter, retrospective, observational post-authorization study EPA-OD study. Investigators will include all consecutive adult patients diagnosed with HER2-negative MBC who have started treatment with nab-paclitaxel monotherapy no further than the third line of chemotherapy for metastatic disease during the past 3 years 2012-2014. These patients must meet all the inclusion criteria and none of the exclusion criteria established in this protocol. 