Trial With Eribulin or Eribulin+ Endocrine Therapy in Locally-recurrent or Metastatic Breast Cancer Patients

Inclusion Criteria:

* ER-positive and/or PR-positive breast cancer.
* HER2-negative breast cancer.
* Unresectable locally advanced or metastatic breast cancer.
* Confirmed disease progression while in the last aromatase inhibition-containing regimen in the metastatic setting.
* At least one taxane or anthracycline regimen in either the adjuvant or the neoadjuvant setting.
* Patients with no prior line of chemotherapy in the metastatic setting.
* At least 1 and up to 3 prior lines of endocrine therapy in the metastatic setting.
* ECOG score 0 or 1.
* Patients have adequate bone marrow and organ function.
* Patients must have measurable disease (RECIST v.1.1).
* Premenopausal with LHRH analogues for at least 28 days) and postmenopausal women.
* Patients must agree to not breastfeed during the study and for 3 months after the last dose of study treatment.
* Life expectancy greater or equal to 12 weeks.
* Patients agree to collection of blood samples (liquid biopsy) and optional collection of metastatic tumour sample (biopsy) at the time of inclusion and progression (if appropriate).

Exclusion Criteria:

* Have received radiation therapy or limited-field palliative radiotherapy within two weeks prior to Cycle 1, Day 1, or patients who have not recovered from radiotherapy-related toxicities.
* Have received prior chemotherapy for locally advanced or metastatic disease.
* Have peripheral neuropathy grade 2 or greater.
* QTc \> 480 msec on basal assessments, history of congenital or personal history of long QT syndrome, Brugada syndrome, or Torsade de Pointes (TdP), or uncontrolled electrolyte disorders
* Child-bearing potential women not using highly effective methods of contraception.
* Known hypersensitivity to eribulin, endocrine therapy or its excipients.
* Other malignancies within the previous two years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of cervix or breast.
* Known uncontrolled metastases to the central nervous system (CNS) or any progressing CNS disease.
* Have a serious concomitant systemic disorder incompatible with the study.
* Major surgical procedure or significant traumatic injury within 28 days prior to randomization.
* Have received any anti-cancer biology or investigational treatment within 30 days prior to randomization.