Metallothionein expression in normal, hyperplastic, and neoplastic thyroid follicular and parafollicular C cells...

Metallothioneins (MTs) are a set of ubiquitous low molecular proteins with a high affinity for metal ions, such as zinc, copper, and cadmium. MT overexpression can be induced by these metal ions as well as by other endogenous and exogenous factors. In this study, normal, hyperplastic, and neoplastic thyroid tissues of both follicular and C-cell origin were immuno-histochemically investigated with a monoclonal antibody against I- and II-isoforms of MTs. MT immunoreactivity was demonstrated in the follicular epithelium of 19 normal thyroid glands and in all 32 cases of Graves' disease investigated; 26 of 30 follicular adenomas and 25 of 28 follicular carcinomas showed MT immunoreactivity, whereas only 7 of 20 papillary carcinomas were MT-positive (p < 0.0001 ). In 3 of the 7 positive samples, positivity was restricted to follicular areas of differentation. No MT could be immunolocalized in normal and hyperplastic C cells and medullary thyroid carcinomas (n = 20). In mixed medullary-follicular carcinomas (n = 4), MT staining patterns resembled those seen for thyroglobulin. In anaplastic carcinomas, MTs were mainly immunolocalized in nonspindle cell areas. MT expression in thyroid tumors may reflect the different biological behavior of follicular and papillary carcinomas. Antibodies to MTs may also serve as fairly specific immunohistochemical markers of follicular cell differentiation in thyroid neoplasia.