Chitinase-3-like protein 1 (CHI3L1) is secreted by various types of cells, including macrophages, chondrocytes, and certain tumor cells. The exact physiological function of CHI3L1 is still unknown, but it is involved in development and inflammatory diseases such as asthma and tumors. CHI3L1 is a cytokine that promotes Th2 response and is highly expressed in the tumor microenvironment and serum of cancer patients. Elevated expression of CHI3L1 is strongly associated with the stage and outcome of various types of tumors, suggesting that CHI3L1 can serve as a biomarker for disease severity. In animal models of glioblastoma multiforme, treatment with neutralizing antibodies against CHI3L1 has shown effectiveness. CHI3L1 can promote angiogenesis through both VEGF-dependent and VEGF-independent pathways. Additionally, CHI3L1 has been shown to enhance tumor cell survival under gamma radiation.