CRLM affects around 1,600 individuals in Denmark each year. State-of-the-art treatment includes liver resection, RFA treatment, radiation therapy, and chemotherapy. Of all individuals undergoing surgery, 50% will experience local or distant recurrence of the disease within five years. Although liver resection is the gold standard, RFA treatment has evolved considerably in recent years. RFA is a parenchymal-sparing treatment for hepatic malignancies, inducing a localized coagulation necrosis of the tumor. This leads to release of tumor antigens, which activates the patients' immune system. However, many cancer cells, including those from CRLM, have the ability to hide their antigens to the patients' immune systems. Using RFA as immunostimulation prior to surgery, these antigens may become visible to the immune system, which in turn can help eradicating all tumor cells and decrease the risk of tumor recurrence. Combined, this likely improves survival.

220 patients with CRLM planned for surgery will be enrolled in this study. Patients will be randomized to +/- RFA treatment before surgery. Under guidance of ultrasonography, a single-electrode RFA-needle is placed in a CRLM with a diameter of at least 3 cm, which is later going to be resected. In 20 of the patients, we will draw blood samples for determination of immune status both pre- and postoperatively. All patients will be part of a work-up with regular CT-scans.

Endpoints are disease free survival and overall survival. Secondarily, we will examine the effect of RFA treatment of tumors on the innate and adaptive immune system in 20 patients.