The above results, suggesting that circulating gastrin precursors could be of particular importance in the pathogenesis/growth of CRC, should make the study of ZES an attractive model to study their role in CRC, because numerous studies have demonstrated that patients with gastrinoma have high circulating levels of not only amidated gastrin, but also progastrin, amino-, and COOH terminal gastrin fragments, as well as Gly-Gastrin [21,39,265]. This evidence concerns the gene GAST and gastrin-producing neuroendocrine tumor.