Pro-gastrin-releasing-peptide, also known as Pro-GRP, is a gastrin-releasing peptide (GRP) precursor, a neurotransmitter that belongs to the bombesin-related neuromedin B family. GRP stimulates the secretion of gastrin in order to increase the acidity of the gastric acid. Pro-GRP is a peptide composed of 125 amino acids, expressed in the nervous system and digestive tract.[1][2] It is different from progastrin, consisting of 80 amino acids, precursor of gastrin in its intracellular version and oncogene in its extracellular version (hPG80).[3][4]
The presence of GRP in lung cancer samples was identified in 1983.[5] In pathological situations, GRP has mitogenic activity in vitro in many cancers including pancreatic cancer, small cell lung carcinoma, prostate cancer, kidney cancer, breast and colorectal cancer.[6][7][8][9] GRP could operate as an autocrine growth factor. In cancers, GRP induces cell growth and inhibits apoptosis by shutting down the endoplasmic reticulum stress pathway.[10] The mechanisms of the impacted signal pathways have not been established.[11] As early as 1994, research on Pro-GRP as a biomarker for small-cell lung carcinoma began.[12] Because of the very short half-life of GRP (2 minutes), the Pro-GRP is used for measurements and analysis. Since then, Pro-GRP has been used as a tumor marker for patients with small-cell lung carcinoma in limited and extended stages.[13]