Production of gastrin releasing peptide by medullary carcinoma of the thyroid. An immunohistochemical study.

Forty medullary carcinomas of the thyroid (MCT) with documented calcitonin (CT) production were studied immunohistochemically for the production of gastrin releasing peptide (GRP), a mammalian counterpart of amphibian bombesin. GRP-positive cells, revealed by an unlabelled peroxidase-antiperoxidase immunoenzyme histochemistry were found in 81% (34/40) of the MCTs. Variable numbers of tumor cells in positive MCTs were immunostained for GRP. In 3 cases with Sipple's syndrome, cells in scattered microscopic MCT nodules and hyperplastic intrafollicular C cells of the thyroid were frequently positive for GRP as well as for CT. Non-neoplastic C cells (or CT-positive cells) of the human thyroids were also positive for GRP. In the neoplastic and non-neoplastic C cell system, some cells were confirmed to be immunoreactive with both anti-GRP and anti-CT. All these findings indicate that GRP and CT are closely associated peptide hormones produced by the C cell system.