Inclusion Criteria:

          1. Histologically or cytologically confirmed infiltrating breast cancer

          2. Oligometastatic disease defined as one to three distant metastatic lesions, with or
             without primary tumor, local recurrence, or locoregional lymph node metastases,
             including the ipsilateral axillary, parasternal, and periclavicular regions. All
             lesions must be amenable to resection or radiotherapy with curative intent. Staging
             examinations must have included a PET-CT-scan and a MRI of the liver in case of liver
             metastases. Clustered lymph nodes that can be irradiated with curative intent in a
             single field are defined as a single lesion. Histologic or cytologic confirmation of
             at least one distant metastatic lesion is required.

          3. No prior line of chemotherapy for metastatic disease (a maximum of 3 months of
             palliative endocrine therapy is allowed).

          4. The tumor must be HER2-negative (either score 0 or 1 at immunohistochemistry or
             negative at in situ hybridization in case of score 2 or 3 at immunohistochemistry).

          5. The tumor is deficient in homologous recombination and/or the patient has a
             deleterious germline BRCA1 or BRCA2 mutation.

          6. At least stable disease of all tumor lesions after three courses of induction
             chemotherapy

          7. Age ≥18 years

          8. World Health Organisation (WHO) performance status 0 or 1

          9. Adequate bone marrow function (ANC ≥1.0 x 109/l, platelets ≥100 x 109/l)

         10. Adequate hepatic function (ALAT, ASAT and bilirubin ≤2.5 times upper limit of normal)

         11. Adequate renal function (creatinine clearance ≥60 ml/min)

         12. If clinically recommended echocardiography, MUGA, or MRI to evaluate if LVEF ≥50%;

         13. Signed written informed consent

         14. Able to comply with the protocol

        Exclusion Criteria:

          -  No malignancy other than breast cancer, unless treated with curative intent without
             the use of chemotherapy or radiation therapy

          -  No current pregnancy or breastfeeding. Women of childbearing potential must use
             adequate contraceptive protection.

          -  No concurrent anti-cancer treatment or investigational drugs