Chitinase-3 like-protein-1 (CHI3L1), one of the CLPs, also has been named YKL-40 in humans and breast regression protein 39 (BRP-39) in mice, is common in both prokaryotes and eukaryotes. Following its initial discovery in the culture supernatant of the osteosarcoma cell line MG63, it was subsequently detected in human chondrocytes, synoviocytes, and vascular smooth muscle cells. In fact, CHI3L1 is produced by a multitude of cells, including macrophages, neutrophils, fibroblast-like cells, hepatic stellate cells, endothelial cells, and cancer cells. CHI3L1 is overexpressed in many human cancer types and animal tumor models, for instance, oligodendroglia, glioblastoma, osteosarcoma, sarcoma, colon, and gastric cancers (GCs). Elevated serum levels of CHI3L1 have been found to be associated with poor prognosis and shorter survival in patients with metastatic cancer. Consequently, CHI3L1 has been increasingly proposed as a sensitive biomarker and an attractive therapeutic target for several certain types of cancers.