CHI3L1 and cancer: In addition, one study showed that CHI3L1, one of the two most abundant exosomal proteins released by macrophages, can induce pancreatic ductal adenocarcinoma cellular resistance to gemcitabine through ERK (extracellular-signal-regulated kinase) activation [40], indicating that CHI3L1 might be a key player in cancers or inflammatory diseases.