During fetal development, it acts as a growth factor for chondrocytes and fibroblasts, with differential expression during the formation of bones and joints (26), but YKL-40 is also expressed in some cancers, and although no direct correlation between YKL-40 expression in tumor tissue and corresponding serum/plasma levels has been demonstrated, elevated values of the latter are correlated with a poor prognosis (27). The gene discussed is CHI3L1; the disease is cancer.