Gastrin-releasing peptide immunoreactivity in medullary thyroid carcinoma

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Abstract
Two cases of gastrin releasing peptide (GRP)‐producing medullary thyroid carcinoma are presented. Immunohistochemical examination revealed the presence of GRP‐like immunoreactivity (IR‐GRP) in the primary tumor tissues. High concentration of IR‐GRP was also demonstrated in extracts of the primary tumors by radioimmunologic means with use of a GRP‐specific antiserum. Chromatographic analysis showed that the immunoreactivity was composed of at least two molecular forms: one behaved as synthetic porcine GRP on Sephadex G‐50 gel filtration and the other as porcine GRP (14–27), a C‐terminal active fragment of GRP. The IR‐GRP was shown not to be attributed to bombesin‐like immunoreactivity. Substance P‐like immunoreactivity was not detected in the tumor tissues by either immunohistochemical or radioimmunologic means. This is, as far as the authors are aware, the first finding of IR‐GRP as an ectopic product in medullary carcinoma.