In Situ Hybridization and Immunohistochemistry Study of Thyroid Peroxidase Expression in Thyroid Tumors

Malignant thyroid tumors reportedly exhibit an anomaly in thyroid peroxidase (TPO) resulting in a lower affinity for monoclonal antibody 47 (mAb 47) in immunohistochemistry studies. The purpose of the present study was to compare TPO immunostaining in normal, benign, and malignant thyroid tissue with expression of mRNA sequences in four exons of the molecule including the epitope of mAb 47. TPO immunostaining was performed using mAb 47 and a polyclonal antibody (pAb). Messenger RNA expression was investigated by in situ hybridization using probes specific for mRNA sequences in exons 2,12 (epitope of mAb), 15, and 17. As expected, pAb immunostaining was significantly positive on all benign tumors and 50% of carcinomas. With mAb 47, little or no immunostaining was observed in 16 of 17 carcinomas while significantly positive immunostaining was found in normal tissue and benign tumors. In situ hybridization showed a decrease and heterogeneity in the expression of all mRNA sequences in carcinomas as compared t...