As GLP-1 analogues remain contraindicated in patients with medullary thyroid cancer and in patients with history of multiple endocrine neoplasia syndrome type 2, caution should be used with the use of DPP-4 inhibitors in the management of diabetes in patients with a known history of neoplasm, considering the similar mechanism of action of DPP-4 inhibitors and GLP-1 analogues and the relation of carcinoid tumors to the other NET. The gene discussed is GCG; the disease is diabetes mellitus.