GRP and prostate cancer: Mechanistically, the growth-promoting function of neuroendocrine tumor cells may be mediated by the paracrine effects of peptide hormones such as bombesin/gastrin-releasing peptide family of neuropeptides, which are secreted from neuroendocrine tumor cells and could stimulate androgen-independent survival, growth and metastasis of the neighboring luminal type prostate cancer cells [47] (Figure 1).