Observation of Medical Treatments in MBC HER2-negative Patients

In particular, the attention will be on those factors, largely discussed in the literature, that predominantly guide the choice among different therapeutic approaches such as: * metastatic sites; * hormone receptor status; * disease-free interval; * grading; * response to a previous treatment with hormonal therapy or chemotherapy. The primary objective is the description of medical therapeutic strategies for the first, the second and the subsequent lines of chemotherapy in a cohort of patients with HER2-negative metastatic breast cancer and the evaluation of the possible correlation between the choice of treatment, in the adjuvant phase or for the metastatic disease and also for the patients' characteristics (age, menopausal status, comorbidity). the secondary objectives are: * Analyze the "Time to Treatment Change", defined as the interval of time that elapses from the start of chemotherapy to the discontinuation or the occurrence of any other event. This finding is of a particular clinical relevance, since randomized trials using the "Time To Progression" (TTP) as a measure of effectiveness of the treatment in the study, but this time parameter may not correspond to what is observed in clinical practice, where the revaluations of disease are not conducted at preset intervals as is in the case of controlled clinical trials. * Evaluate the correlation between the characteristics of the patients and the choice of the type of chemotherapy. * Assess the potential correlation between the type of adjuvant therapy and the type of response obtained with the first-line treatment and between the answer to this last therapy line and second/third one. * Assess the adherence to the literature's recommendations (Consensus Conferences and Guide-lines) of the choices between the sequential therapy vs the combination therapy in different lines of treatment (first, second, third line) of the metastatic disease.