Chromogranin A is a member of the granin family of neuroendocrine secretory proteins. It is located in secretory vesicles of neurons and endocrine cells. Chromogranin A is the precursor to several functional peptides including vasostatin, pancreastatin, catestatin and parastatin. These peptides negatively modulate the neuroendocrine function of the releasing cell (autocrine) or nearby cells (paracrine). CgA is one of the most used tumor markers in NET's (neuroendocrine tumors) , and elevated CgA concentrations have been demonstrated in serum or plasma of patients with different types of these tumors. However, CgA is not a tumor-specific antigen for NETs, and an abnormal concentration has been described in some non-malignant diseases such as renal failure, heart failure, proton pump inhibition, gastritis, hypertension, or patients with liver diseases.