GPR68 and medullary thyroid gland carcinoma: Interestingly, and likely because GPR68 is also expressed in non-neoplastic endocrine and neuroendocrine cells, a high percentage of GPR68-positive cases was observed in tumours of endocrine or neuroendocrine origin, such as growth hormone-producing pituitary adenomas, bronchopulmonary and gastroenteropancreatic neuroendocrine tumours, pheochromocytomas, paragangliomas, and medullary thyroid carcinomas.