CGA and neuroendocrine neoplasm: The situation is even more complex in the case of neuroendocrine tumors or tumors with neuroendocrine differentiation, as in both these cases the tumor vasculature can be exposed not only to CgA molecules released by neuroendocrine system into the blood, but also to CgA released in tumor microenvironments (and then into the blood) by neoplastic cells.