BDNF and head and neck squamous cell carcinoma: It was reported that TRKB and BDNF are both highly expressed in more than 50% of human head and neck squamous cell carcinoma (NHSCC) tumors [32], and that the positive expression rates of TRKA, TRKB, and TRKC in human OSCC reach 90.2% (92/102 cases), 31.4% (32/102 cases), and 47.0% (48/102 cases), respectively [37].