The incidence of colorectal cancer (CRC) ranks third in the world among malignant tumors, and CRC is also the second leading cause of cancer-related deaths. There are about 1.8 million new cases of CRC and 881,000 deaths annually. 1 It is estimated that by 2030, the global burden of CRC will increase by 60%. 2 At present, early detection technology has greatly assisted early diagnosis and intervention of CRC, but about 25% of patients are nonetheless diagnosed as stage IV. 3 In the past 15 years, treatment strategies for metastatic colorectal cancer (mCRC) have improved, but the 5-year overall survival rate (OS) is still only 14%, 4 posing a serious threat to public health. Immunotherapy is a new emerging tumor treatment method following surgical resection, chemoradiotherapy, and biological targeted therapy. Immunotherapy can eliminate tumor cells and inhibit tumor growth and metastasis by activating the immune system and exerting the immune capacity of the tumor microenvironment (TME). Immunotherapy is highly specific, which can not only damage normal cells but can also stimulate immune memory. Immunotherapy has become the focus of CRC treatment research in recent years. Immune checkpoint inhibitors (ICIs) are the most widely used form of immunotherapy.At present, the FDA has approved ICI treatment for patients with mismatch repair-deficient (dMMR) / microsatellite instability-high

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