Treatment principles for metastatic disease Treatment of non-concurrent metastatic disease Examination of metastatic disease includes enhanced CT or MRI, PET/CT may also be considered for rapid identification of other extrahepatic metastases, determination of RAS status, and consideration of BRAF testing. Treatment of non-concurrent metastatic disease differs from concurrent metastatic disease in that treatment of resectable disease includes resection and 6 months of perioperative chemotherapy, with regimens chosen based on prior chemotherapy history. FOLFOX or CapeOX is the preferred regimen for those with no history of chemotherapy, and FLOX, capecitabine, and 5-FU/LV are also options. There are some cases where perioperative chemotherapy is not recommended, especially for those with a history of oxaliplatin chemotherapy who can be resected with the option of observation, and observation is also appropriate for tumors growing in neoadjuvant therapy. Chemotherapy is to be administered for unresectable disease, and HAI therapy is optional for those with only liver metastases . Patients receiving palliative chemotherapy should be evaluated with CT or MRI every 2-3 months. Post-treatment surveillance After curative surgery and adjuvant chemotherapy, post-treatment surveillance should be performed to assess possible treatment complications, detect potentially resectable recurrences, and identify new tumors in a non-invasive stage. Studies have shown that 95% of recurrences occur within 5 years. The intensity of surveillance adopted for patients at different stages is still controversial. Possible hazards of long-term follow-up include radiation exposure, nonstop follow-up, and psychological stress from false-positive results. The stage I patient committee recommends colonoscopy at 1 year, 3 years, and then every 5 years, except when progressive adenomas (villous polyps, polyps >1 cm, or high-grade abnormal growths) are found, which should be performed annually. The committee recommends history and physical examination every 3-6 months for 2 years and then every 6 months for 3 years for stage II/III patients after successful treatment. CEA examination is recommended at baseline, every 3-6 months for 2 years, and every 6 months for 3 years. Colonoscopy is recommended for stage II/III patients 1 year after resection (or 3-6 months after surgery if not performed preoperatively due to obstruction), 3 years, and then every 5 years, unless progressive adenomas (villous polyps, polyps >1 cm, or high-grade abnormal hyperplasia) are found and should be performed annually. More frequent colonoscopies should be performed in patients younger than 50 years of age. Patients with Lynch syndrome should be screened more frequently. CT of the chest, abdomen and pelvis is recommended once a year for 5 years, mainly for stage II/III patients at high risk of recurrence. routine monitoring of CEA and CT is not recommended after 5 years, and PET/CT is not the ideal routine monitoring test. Colonoscopy is mainly to identify and remove non-concurrent polyps, as those with a history of colon cancer are at increased risk of developing duplex cancer, especially within 2 years after resection. CT is used to monitor for the presence of potentially resectable metastatic disease, mainly lung and liver. Surveillance of patients with curative treatment in stage IV is the same as for stage II/III patients, but certain tests should be more frequent. The committee recommends chest, abdominal, and pelvic enhancement CT every 3-6 months for the first 2 years after adjuvant therapy and then every 6 months for 3 years; conventional PET/CT is not recommended. Colonoscopy, CT of the chest, abdomen and pelvis, physical examination, and also PET/CT may be considered for patients with increased CEA. If imaging is normal and CEA is constantly elevated, repeat CT every 3 months until disease is detected or CEA levels are stable or decreasing. Studies have shown that half of the increase in CEA after R0 resection is a false positive, and when CEA > 35ng/ml is usually a true positive.