α‐neoendorphin‐like immunoreactivity in medullary carcinoma of the thyroid

α-Neoendorphin-like immunoreactivities (α-NE-IR) were demonstrated in tissues from three patients with medullary carcinoma of the thyroid (MCT). A large amount of α-NE-IR was detected in the extracts of primary tumors and metastatic lymphatic tissues by a highly sensitive and specific radioimmunoassay (RIA). Gel filtration analyses showed two different molecular-weight forms of the α-NE-IR: One eluted at the void fraction and the other at the position of [125I]-α-NE on Sephadex (Pharmacia Fine Chemical, Uppsala, Sweden) G-50 chromatography. Immunohistochemical examination revealed the presence of α-NE-IR in the C-cell carcinoma. These data presumably reflect that α-NE, the opioid peptide derived from preproenkephalin B, is synthesized in the MCT. Cancer 59:277–280, 1987.