Importantly, glucagon-expressing neuroendocrine tumors as well as microadenomas were present in the pancreases of T2DM donors who have been treated with sitagliptin or exenatide for 1 year or more, implying the possible long-term deleterious potentiation of incretion in developing neuroendocrine tumors (28). Here, GCG is linked to type 2 diabetes mellitus.