SALMON CALCITONIN-LIKE IMMUNOREACTIVITY IN HUMAN NEUROENDOCRINE TUMORS

Background: Salmon calcitonin (sCT) injection into rats has been repor ted to induce pituitary tumours. We have demonstrated the co-existence , in the rat-derived cl-TSH cell line, of an sCT-like peptide, as well as a receptor for sCT. Aim: This was to investigate the possible exis tence of sCT-like immunoreactivity (sCT-LI) in human neuroendocrine tu mours. Methods: A collection of human neuroendocrine tumours was teste d, using a highly specific antibody for sCT. Immunostaining was abolis hed by preabsorption with sCT at concentrations higher than 1 mu g/ml. However, as immunofluorescence was still obvious at the highest conce ntration (100 mu g/ml) of hCT employed, any significant cross-reactivi ty was excluded. Results: Of the human pituitary null cell tumours stu died, positive staining was obtained in 2 out of 12, suggesting a simi larity between the rat and human pituitary glands. None of the other p ituitary rumours tested showed sCT-LI (these included 8 corticotroph r umours, 6 prolactinomas and 2 somatotroph tumours). This work was exte nded to medullary thyroid carcinomas (MTCs) and a further group of neu roendocrine tumours, looking for the specificity of this sCT-LI among the various APUDomas. All the tested MTCs (n=14) expressed sCT-LI, whi le none of the examined phaeochromocytomas (n=23), intestinal carcinoi ds (n=14), lung carcinoids (n=16), stomach carcinoids (n=2), rectal ca rcinoids (n=2), gastrinomas (n=4), insulinomas (n=12), oat cell carcin omas (n=7), carotid body rumours (n=9), VIPomas (n=3), or a glucagonom a (n=1) expressed sCT-LI. This indicates that this sCT-LI might be uni que to MTC (and possibly the pituitary). Conclusion: The possible exis tence of the most potent form-of CT may provide an explanation for the vasomotor disturbances in MTC and may be a potential new tumour marke r for MTC. Phylogenetically, the presence of a lower form of CT in mam malian tissues would give an insight into the conservation of the CT p eptide family in evolution.