The efficiency of T cell based immunotherapies is affected by the insufficient migration and activity of tumor specific effector T cells in the tumor. Aim of this phase I/II clinical trial is to evaluate whether a neoadjuvant, low dose radiotherapy can improve T cell connected anti tumor immune response in colorectal liver metastases.

The primary endpoint is the number of tumor infiltrating T cells. Furthermore the T cell activity in situ, the number of regulatory T cells and the frequency of tumor reactive T cells in the blood and bone marrow will be examined.

Inclusion Criteria:

• Ability of subject to understand character and individual consequences of the clinical trial
• Written informed consent (must be available before enrolment in the trial)
• Age ≥ 50 years
• Radiological urgently suspected colorectal liver metastasis

Exclusion Criteria:

• second malignancy
• Pregnancy and lactation
• no prior liver radiation
• liver metastasis must be resectable