NGF and cholangiocarcinoma: Some experimental results proved that NGF expressed in CCA could facilitate CCA cell proliferation[23,24]; while NGF secreted by CCA cells could facilitate autospecific proliferation, it might also bind to TrkA receptors expressed in the perineurium, which supplies an adaptive microenvironment and chemical tropisms for the growth of nerve cellular axons, facilitating axon growth in the direction of the tumor[25].