Radioembolisation is a known method for the treatment of liver tumors and or livermetastases. Currently small beadlets called microspheres are used that are loaded with the beta radiation emitting Yttrium-90. Holmium-166 microspheres have different physical characteristics including good visualisation in gammacameras due to the gamma emission. Because of the higher specific activity higher radiation doses to the liver will be used compared to the standard Yttrium treatment. It is hypothesized that higher doses of irradiation have an improved antitumor effect.

List of inclusion criteria:

• 1. Patients must have given written informed consent.
• 2. Female or male aged 18 years and over.
• 3. Diagnosis of metastatic malignancy to the liver and no detectable malignant disease outside the liver or diagnosis of metastatic malignancy to the liver with limited disease outside the liver (i.e. liver-dominant disease) defined as the sum of the diameters of all metastases in the liver to be more than 200% of the sum of the diameters of all soft tissue lesions outside the liver.
• 4. Patient is not amenable for standard therapies (other than radioembolisation) or patient refuses standard therapies for reasons of toxicity
• 5. Life expectancy of 12 weeks or longer.
• 6. World Health Organisation (WHO) Performance status 0-2 (see Appendix III).

List of exclusion criteria:

1. Brain metastases or spinal cord compression, unless irradiated at least 4 weeks prior to the date of the experimental treatment and stable without steroid treatment for at least 1 week.
2. Radiation therapy within the last 4 weeks before the start of study therapy.
3. The last dose of prior chemotherapy has been received less than 4 weeks prior the start of study therapy.
4. Major surgery within 4 weeks, or incompletely healed surgical incision before starting study therapy.
5. Any unresolved toxicity greater than National Cancer Institute (NCI), Common Terminology Criteria for Adverse Events (CTCAE version 4.0, see Appendix II) grade 2 from previous anti-cancer therapy.
6. Serum bilirubin > 1.5 x Upper Limit of Normal (ULN).
7. Glomerular filtration rate <35 ml/min, determined according to the Modification of Diet in Renal Disease formula.
8. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase (ALP) > 5 x ULN.
9. Leukocytes < 4.0 109/l and/or platelet count < 150 109/l.
10. Significant cardiac event (e.g. myocardial infarction, superior vena cava (SVC) syndrome, New York Heart Association (NYHA) classification of heart disease ≥2 within 3 months before entry, or presence of cardiac disease that in the opinion of the Investigator increases the risk of ventricular arrhythmia.
11. Pregnancy or breast feeding (women of child-bearing potential).
12. Patients suffering from diseases with a increased chance of liver toxicity, such as primary biliary cirrhosis or xeroderma pigmentosum.
13. Patients suffering from psychic disorders that make a comprehensive judgement impossible, such as psychosis, hallucinations and/or depression.
14. Patients who are declared incompetent.
15. Previous enrolment in the present study or previous treatment with radioembolisation.