CHI3L1 and cancer: YKL-40-inhibiting small compounds such as caffeine, theophylline, chitin (β-(1-4)-poly-N-acetyl D-glucosamine), and siRNA complex are known to be effective in reducing tumor growth and metastasis in diverse kinds of cancers through down-regulation of signaling pathways, including PI3K/AKT, STAT3, and NF-kB, downstream of YKL-40 [10,11,12,13,14,15].