Gastrin-releasing peptide-like immunoreactivity in medullary thyroid carcinoma

Gastrin-releasing peptide, the mammalian counterpart of amphibian bombesin, has been found to be present in high concentration by radioimmunoassay in eight histologically confirmed medullary thyroid carcinomas and to be undetectable in postmortem normal thyroid tissue. Chromatographic analysis of the tumor extracts by gel permeation revealed two major peaks of gastrin-releasing peptide-like immunoreactivity (GRP-LI). However, reverse-phase high-pressure liquid chromatography demonstrated three immunoreactive peaks of GRP-LI. None of these immunoreactive peaks was coeluted with synthetic porcine GRP or amphibian bombesin, but one of the peaks exactly emerged in the position of neuromedin C (C-terminal decapeptide of GRP). Sections from nine primary or secondary tumours were immunostained for GRP using a peroxidase/anti-peroxidase technic. All the medullary thyroid carcinomas were shown to contain GRP-LI, specifically localized to the tumor cells. This immunoreactivity is elevated in plasma from some patients with this malignancy, raising the possibility that it may be used as an additional tumor marker.