Abstract: Colorectal cancer is one of the common malignant tumors worldwide, and ranks second in tumor-related deaths. The treatment methods are mainly surgery, radiotherapy, and chemotherapy. With the continuous exploring mechanisms of proliferation, invasion, and metastasis in colorectal cancer cells and the advancement of medical technology, there are now more and more treatment options and postoperative monitoring methods for colorectal cancer. However, the postoperative recurrence rate and mortality rate of patients are still high, and the prognosis is poor. At present, the assessment of the condition mainly relies on imaging examination and tumor marker screening, but there are certain limitations and delays in monitoring disease recurrence. Therefore, it is particularly important to find suitable clinical indicators to assist in monitoring disease recurrence without increasing the economic burden on patients. In recent years, there have been continuous studies suggesting that chronic inflammation is related to tumors. The systemic immune-inflammation index(SII)based on platelets, neutrophils, and lymphocytes has shown great application prospects and may become a simple, economical, reproducible, and non-invasive reference index for the prognosis of colorectal cancer. This article will review the research results related to SII and prognosis of colorectal cancer in recent years.

Key words: Colorectal Cancer, Prognosis, Adjuvant chemoradiotherapy, Systemic immune-inflammation index