BDNF and cancer: The potential involvement of neurotrophins in various cancers, including myeloma (Pearse et al., 2005), breast cancer (Vanhecke et al., 2011), lung cancer (Ricci et al., 2001), medullary thyroid carcinoma (McGregor et al., 1999), hepatocellular carcinoma (Yang et al., 2005), gastric cancer (Okugawa et al., 2013), and even gliomas (Birnbaum et al., 2007; Johnston et al., 2007), has also been recognized for a long time.