Current guidelines and major institutions recognize high-risk factors including poor differentiation (grade 3/4 differentiation, such as hypofractionated, indolent cell carcinoma, mucinous adenocarcinoma, etc.), vascular (vascular/lymphatic) infiltration, perineural infiltration, T4 (penetration of the entire bowel wall or infiltration of surrounding organs/structures), obstruction, perforation, positive or indeterminate margins, and <12 lymph nodes sent for examination, classifying patients with any of these factors as "high-risk stage II colon cancer" and the guidelines recommend not only postoperative adjuvant chemotherapy but also oxaliplatin-containing combination chemotherapy. After 2009, studies on the benefit of chemotherapy for stage II colon cancer have again found that dMMR (mismatch repair protein deletion) is a marker of good prognosis, with a 5-year survival rate of 80% after surgery alone, followed by the finding that stage II colon cancer with dMMR not only does not benefit from adjuvant chemotherapy with 5-FU, but may have the opposite effect. Therefore, since 2010, guidelines have recommended that all stage II colon patients (<50 years of age) to be treated with fluorouracil-based monotherapy should be tested for MMR and, in the case of dMMR, should be observed without chemotherapy. Another synonym for dMMR is the well-known MSI-H (microsatellite high instability), which results from mutations in the MMR gene, insertion or deletion of DNA repeat units resulting in high MSI instability and MMR protein deletion. The pathology community has identified similar clinicopathological features of MSI-H colon cancer, which are called MSI-H-like pathological features. The overall prognosis of MSI-H tumors is good. In general, poor differentiation (high grade) is a characteristic of poor prognosis, except in MSI-H tumors, and the MSI-H group should be excluded when determining the need for adjuvant chemotherapy in stage II colon cancer based on high risk factors for histologic differentiation. PS: A study at the 2012 ESMO meeting had mixed results, and a meta-analysis by the DCCG showed that among patients with stage IV metastatic colorectal cancer, patients with dMMR had a significantly worse prognosis than those with pMMR (median progression-free survival, 6.2 months versus 7.1 months, HR=1.23, P<0.05) for unknown reasons. BRAF mutations were an indicator of poor prognosis (overall survival, 11.3 versus 16 months, HR=1.81, P<0.05), while pmmr patients with braf wild type had the best prognosis. Based on this result, we concluded that the prognostic validity of mmr was diminished. < span="">Some scholars have analyzed the significance of dMMR as valid for those with genetic background, such as hereditary non-polyposis colorectal cancer. PS: 2013 Opinion – Stage II dMMR has a good prognosis and chemotherapy is not recommended; stage III dMMRers with inconsistent predictive data for 5-Fu single agent efficacy, combined with OXA chemotherapy, do not need to be tested.