Immunocytochemistry of canine thyroid tumors

Immunocytochemical studies using the peroxidase-antiperoxidase method with commercial antibodies against thyroglobulin, calcitonin, calcitonin gene-related peptide (CGRP), neuron specific enolase (NSE), somatostatin, and neurotensin were performed on 38 Bouin-fixed, paraffin-embedded canine thyroid tumors obtained from necropsy and surgical files from 2 Ecoles Nationales Vétérinaires (Alfort and Nantes, France) and from the Laboratoire d'Histo-Cytopathologie Vétérinaire, Maisons-Alfort (France). The tumors consisted of two follicular adenomas, nine follicular carcinomas, nine solid carcinomas, 12 follicular-compact-cellular carcinomas, and six C-cell carcinomas. All 32 follicular-cell tumors were stained positively for thyroglobulin, half of them had weak to moderate positive immunoreactivity for NSE, and all histologic patterns were represented. They had no immunoreactivity for somatostatin or neurotensin. Four C-cell carcinomas had a solid alveolar pattern, while two had a pseudo follicular pattern characterized by uneven, often coalescent, pseudo-follicular formations with a multilayered epithelium surrounding a cavity that often contained red blood cells. Four C-cell carcinomas had uneven immunoreactivity for calcitonin, while all six were positive for CGRP or NSE. Immunoreactivity for CGRP was stronger or more widespread than positivity for calcitonin when both occurred in the same tumor. Some cells of three C-cell carcinomas had positive immunoreactivity for somatostatin. No immunoreactivity for neurotensin was detected. Seven tumors of follicular cell origin contained a few cells positive for calcitonin or CGRP, while three C-cell carcinomas had a few cells positive for thyroglobulin. These tumors were considered to contain entrapped remnants of normal thyroid tissue rather than being dual hormone producing tumors.