The goal of this multicentre clinical pilot study is to investigate the feasibility of the addition of Ho-166 radioembolization to chemotherapy in patients with liver metastastic breast cancer.

Participants will receive a mapping angiography and Ho-166 radioembolization. Chemotherapy will be stopped 2-5 prior to radioembolization and continuation of chemotherapy will be evaluated at 2 weeks post-radioembolization.

Inclusion Criteria:

• Women >18 years
• Patients with hormone positive and HER2 negative liver metastatic breast cancer
• No extra-hepatic disease progression at evaluation of at least second line systemic chemotherapy
• Suitable for TARE evaluated after the mapping angiography
• Measurable target tumors in the liver according to RECIST 1.1
• Liver tumor burden <50 %
• ECOG performance score 0 to 1
• Laboratory parameters: neutrophils >1000/μL; thrombocyte count >1000000 μL; eGFR >45/mL/min/1.73 m2; albumin > 3.0 g/dl, bilirubin < 1.5x ULN (unless Gilbert syndrome); aminotransferase (ALAT/ASAT) <3.0 ULN
• Able to read Dutch

Exclusion Criteria:

• Life expectancy ≤3 months
• Patient eligible for other curative local liver therapy (ea. surgery, ablation)
• Brain, pleural, peritoneal or extensive extra-hepatic visceral metastases
• Other life-threatening disease (i.e. Dialysis, unresolved diarrhea, serious unresolved infections (HIV, HBV, HCV etc.))
• Contraindication for angiography or MRI
• Significant toxicities due to prior cancer therapy that have not resolved before the initiation of the study, if the investigator determines that the continuing complication will compromise the safe treatment of the patient
• Prior or planned embolic intra-arterial liver directed therapy (TACE, TAE, TARE)
• Prior or planned external or internal radiation therapy of the liver
• Cirrhosis or portal hypertension
• Main portal vein thrombosis
• Intervention for, or compromise of, the Ampulla of Vater
• Ascites (except minor focal ascites)
• Baseline use of analgesics for abdominal pain
• Pregnancy (Women at childbearing potential need at least one form of birth control) and breastfeeding
• Flow to extra hepatic vessels not correctable by reposition or embolization
• Estimated dose to the lungs greater than 30 Gy in a single administration or 50 Gy cumulatively
• Target tumoral absorbed dose of < 90Gy or an absorbed dose to the normal liver parenchyma of >50Gy (in case of whole liver treatment)