Previous studies have presented neurotransmitters and neurotrophins (e.g., substance P [80], nerve-growth factor (NGF) [81,82,83] and brain-derived neurotrophic factor (BDNF) [84]), chemokines (e.g., CX3CL1 [85] and CCL2 [86,87]), extracellular vesicles [66,88], and Schwann cells [52,89] as key players in cancer–nerve crosstalk. The gene discussed is BDNF; the disease is cancer.