NGF and lip and oral cavity carcinoma: NGF has been shown to play a role in tumour proliferation and perineural spread (PNS) in oral cancer [134] and it has been shown that oral squamous cell carcinoma (OSCC) with evidence of PNS has an increased expression of NGF and TrkA and this data suggested that NGF and TrkA are correlated with the development of PNS [134].