The aim of this study was to assess the clinical sensitivities of the tumor markers chromogranin A (CgA), urinary 5-hydroxyindoleacetic acid (5-HIAA) and alkaline phosphatase (AP) in neuroendocrine tumors (NETs) of the GastroEnteroPancreatic-(GEP-) system depending on tumor primary location and metastatic spread. This evidence concerns the gene CGA and neoplasm.