Among the 30 tumour entities investigated, we identified significant GPR19 expression (mean IRS value ≥ 3) only in lung tumours, especially in those with a neuroendocrine background, such as TC, AC, and SCLC, and in medullary thyroid carcinomas, parathyroid adenomas, and pheochromocytomas, which also belong to the neuroendocrine tumour entities. The gene discussed is GPR19; the disease is medullary thyroid gland carcinoma.