In Pan-NETs, both functioning and non-functioning Pan-NETs showed serum CgA levels up to 60–80 times the upper normal levels, particularly in Zollinger–Ellison syndrome in MEN-1 cases with serum CgA levels being 80–100 time higher than the upper normal levels [45,48]. The gene discussed is CGA; the disease is multiple endocrine neoplasia type 1.