Adult patients aged 18-80 years old, American Society of Anesthesiologists physical status I-III, who were scheduled for elective colorectal cancer surgery under general anesthesia were recruited for this study. They were randomized to receive opioid-free anesthesia (OFA), opioid-sparing anesthesia (OSA) and opioid-based anesthesia (OA) group. Blood samples were collected pre-surgery and 24h post-surgery. As primary endpoint, serum neutrophil myeloperoxidase (MPO) and citrullinated histone3 (CitH3) was measured. The secondary endpoints included the effects of postoperative serum on colorectal cancer (CRC) cells malignancy, numerical rating scale (NRS) scores, postoperative adverse events and recovery profiles. For OA group, intraoperative remifentanil and sufentanil were used and postoperative patient controlled intravenous analgesia (PCIA) was performed with 0.5μg/ml of sufentanil and 0.75 mg/mL flurbiprofen, and the PCIA was stopped 48 h after surgery. For OSA group, remifentanil and sufentanil were used only for anesthetic induction and the patient received ultrasound-guided transversus abdominis plane (TAP) nerve blockwas performed. Patient controlled intravenous analgesia (PCIA) was performed with 1mg/mL of oxycodone and 0.75 mg/mL flurbiprofen after surgery, and the PCIA was stopped 48 hours after surgery. For OFA group, intraoperative epidural anesthesia combined with general anesthesia was used, and esketamine, lidocaine and dexmedetomidine for analgesia. Patient controlled epidural analgesia (PCEA) was used and terminated 48 hours after surgery.