Assessing ImmunoResponse Post Eribulin: Eribulin and Immunogenicity in Advanced Breast Cancer

Inclusion Criteria: * Written informed consent prior to beginning of trial specific procedures * Subject must be female and aged ≥ 18 years on day of signing informed consent * ECOG 0-1 * Histologically confirmed, HER2 negative breast cancer determined by core biopsy of tumor lesion. Human epidermal growth factor receptor 2 (HER2) negativity is defined as either of the following by local laboratory assessment: In situ hybridization (ISH) non-amplified (ratio ≤ 2.2), or IHC 0 or IHC 1+. * Indication for chemotherapy * Previous therapy with one chemotherapy line * Target lesion (RECIST 1.1) * Adequate organ function defined as: Creatinine Clearance \> 50 ml/min ANC ≥ 1.5 x 10 3 /μL Thrombocytes \> 100 x 10 3 /μL Exclusion Criteria: * HER2 positive disease * Indication for an anti-hormone treatment * Active infection requiring systemic therapy. * Active autoimmune disease or other diseases that requires systemic treatment with corticosteroids or immunosuppressive drugs. * History of primary or acquired immunodeficiency (including allogenic organ transplant). * Active or prior documented inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis). * Severely impaired liver function (Child Pugh C) * Hypersensitivity to study medication or any of its components * Neuropathy (PNP) \> Grade 2 (CTCAE 5.0) * Congenital long QT syndrome * Preexisting concomitant use of strong CYP3A4 and CYP2C8 inhibiting or inducing drugs * Life expectancy of less than three months * Pregnancy (contraception is required according tocontraceptive guidance) * Lactation * Known history of following infections: Human immunodeficiency virus (HIV), History of acute or chronic Hepatitis B or Hepatitis C * Has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted. * Does not agree to blood collection