Ten-Fold Elevation of Chromogranin A Level Unrelated to a Neuroendocrine Tumor: A Case Report of the Diagnostic Interference of Proton Pump Inhibitors.

Chromogranin A (CgA) is a well-known biomarker for neuroendocrine tumors (NETs). However, due to its non-specificity, a proper assessment of CgA test results requires a detailed knowledge of the factors, conditions, and medications influencing its serum concentration. We describe a case of a 61-year-old patient presenting with a mass suspicious of a gastrointestinal NET and an exceedingly high level of serum CgA persistent after mass resection.