The aim of this study is to compare the effects of three types of perioperative analgesia on the number of circulating cancer cells (representing minimal residual disease) following radical colon cancer surgery. Patients will be randomized into one of three groups. The intervention group will receive combined regional and general anesthesia during surgery and postoperative epidural analgesia. The two control groups will receive balanced general anesthesia and either morphine-based or piritramide-based postoperative analgesia. We hypothesize that epidural analgesia will be favorable to both piritramide-based and morphine-based analgesia and that piritramide-based analgesia will be favorable to morphine-based analgesia with regard to the number of circulating cancer cells and its development in the early postoperative period.