Second Line ERIbulin Followed by CApecitabine or the Reverse Sequence in HER2-negative Metastatic Breast Cancer Patients

Inclusion Criteria:

* Written informed consent (both for clinical and blood biomarker study)
* Histological diagnosis of HER2 negative MBC
* Females ≥ 18 years
* Measurable disease (according RECIST criteria version 1.1)
* Prior Anthracyclines and Taxanes in either (neo-) adjuvant or metastatic setting, unless the patient was not suitable for one of these treatments
* 1 prior cytotoxic regimen for advanced or MBC (not including adjuvant or neo-adjuvant therapy). Patients with no prior cytotoxic regimens for advanced or metastatic disease will only be allowed if they relapsed during or within 6 months of (neo-) adjuvant cytotoxic therapy that included anathracyclines and/or taxanes (see prior criteria);
* Prior hormonotherapy and Cyclines inhibitors are allowed, so as indicated in the international guidelines for the management of hormone positive breast cancer (ER and/or PR positive);
* ECOG Performance Status ≤ 2
* Absence of angina or heart failure or infarction within 12 months from inclusion
* Adequate bone marrow and organ function as follows (haemoglobin ≥9.0 g/dl; absolute neutrophil count ≥ 1.5x103/mm3; plateled count ≥ 100x103/mm3; bilirubin levels ≤ 1.5 times Upper Limits of Normal
* biliary stenting is allowed to resolve obstruction - Serum Transaminase level ≤ 2.5 times ULN; serum creatinine ≤ 1.5 times ULN;
* Life expectancy of at least 12 weeks;
* If women of childbearing potential (WOCBP) age: effective contraceptive measures must be used during the study treatment period and up to 3 months after the last dose of study drug.

Exclusion Criteria:

* Unability to give informed consent
* Absence of measurable disease
* Concurrent active malignancies (except of in situ carcinoma of the cervix and inactive non-melanoma skin cancer)
* Current active infection;
* Serious pre-existing medical conditions or serious concomitant diseases;
* systemic disorders that would compromise the safety of the patient or her ability to complete the study, at the discretion of the investigator (for example, unstable angina pectoris, or a clinically significant history of cardiac disease or uncontrolled diabetes mellitus);
* Known immunodeficiency virus infection;
* Pregnant or breastfeeding women
* Unable to undergo medical test for geographical, social or psychological reason;
* Active or symptomatic brain metastases;
* Known complete Dihydropyrimidine dehydrogenase (DPD) deficiency (phenotype and/or genotype testing, according to applicable national guidelines, prior to the initiation of treatment with Capecitabine is recommended)
* Recent or concomitant treatment with brivudine (there must be at least a 4-week waiting period between end of treatment with brivudine and start of capecitabine therapy).