The aims of this randomized study were to compare postoperative immune function assessed by NK cell cytotoxicity (NKCC) and interleukin (IL)-2, which is required for proliferation and cytotoxic activities of NK cells; and to evaluate short-term cancer recurrence or metastasis based on postoperative pain management with opioids or with continuous wound infiltration in patients undergoing laparoscopic resection of colorectal cancer. This evidence concerns the gene IL2 and cancer.