CHI3L1 and cancer: YKL-40 belongs to a group of mammalian proteins with an amino acid sequence similar to the 18-glycosyl hydrolase group of bacterial chitinases [6, 7], and is found to be expressed and secreted by chondrocytes, synoviocytes, hepatic stellate cells, vascular smooth muscle cells, neutrophils, while it commonly overexpressed in several types of cancer including breast, colon, kidney, lung, ovarian, prostate, uterine, osteosarcoma, glioblastoma and germ cell tumors [8, 9].