The aim of this study is to identify techniques of perioperative analgesia with the potential to prevent metastasis development in patients undergoing open radical colon cancer surgery. In the early postoperative period, a relationship between metastasis development and the number of circulating cancer cells representing minimal residual disease has been shown. Therefore, effects of epidural, morphine-based and piritramide-based analgesia on the number of circulating cancer cells will be compared at several time points during the peroperative and early postoperative periods. The number of circulating cancer cells will be assessed in peripheral venous blood samples using real-time polymerase chain reaction. Perioperative care will be standardized and patients will be followed by clinical observation, laboratory analyses and monitoring instrumentation daily during their hospital stay.