Chromogranin A as Blood Marker in Cancer Patients

Inclusion Criteria: * Primary well-differentiated G1 and G2 neuroendocrine tumor located in jejunum, ileum, colon, rectum, duodenum, appendix, stomach, or pancreas * Measurable disease according to RECIST criteria (Version 1.1) * Eighteen years of age or older * CT or MRI order obtained and within 4 weeks of CgA measurement * BRAHMS CgA II KRYPTOR baseline measurement available * Patient has discontinued the following treatments for at least 3 weeks before study start: i) proton pump Inhibitors (PPI), ii) corticoids, iii) H2-receptor antagonists * Baseline Eastern Cooperative Oncology Group Performance Scale (ECOG PS) \<2 * Written informed consent signed Exclusion Criteria: * Other active malignancy with the exclusion of melanoma or other cancers that occurred more than 5 years ago * Participation in another clinical trial involving an investigational therapeutic (exception: diagnostic studies and studies evaluating known therapies) * No measurable disease by RECIST criteria (Version 1.1) * Severe renal dysfunction defined as creatinine of 1.5x upper limit of normal (ULN) * Severe liver dysfunction in the absence of liver metastasis defined by aspartate aminotransferase (AST), serum total bilirubin and/or alanine transaminase (ALT) 1.5x ULN; severe liver dysfunction in the presence of liver metastasis defined by AST and ALT over 5x ULN and total bilirubin over 1.5x ULN * Severe gastrointestinal disorders (chronic atrophic gastritis, pancreatitis, inflammatory bowel diseas…