In Pan-NETs, both functioning and non-functioning tumors showed serum CgA levels at 60 ~ 80 times the normal upper levels, particularly in Zollinger-Ellison syndrome in MEN1 cases with serum CgA levels being 80 ~ 100 times higher than the normal upper levels [14,42,43]. This evidence concerns the gene MEN1 and Zollinger-Ellison syndrome.