BDNF and lung cancer: Studies also found that BDNF/TrkB increased metastasis in many malignancies, such as pancreatic ductal carcinoma [29], prostate cancer [30], lung cancer [31], hepatocellular carcinoma [21, 32], colorectal cancer [33–34], gastric cancer [35], choriocarcinoma [36], ovarian cancer [37], and multiple myeloma [38].