CHI3L1 and osteosarcoma: Following its initial discovery in the culture supernatant of the osteosarcoma cell line MG63,1 it was subsequently detected in human chondrocytes, synoviocytes, and vascular smooth muscle cells.2,3 In fact, CHI3L1 is produced by a multitude of cells, including macrophages, neutrophils, fibroblast-like cells, hepatic stellate cells, endothelial cells, and cancer cells.4–9 For the moment, extracellular matrix (ECM) changes, miRNAs, growth factors, cytokines, stress, and drugs have been reported to be effective regulators of the synthesis and secretion of CHI3L1.10–13