IMMUNOHISTOCHEMICAL LOSS OF THYROID PEROXIDASE IN PAPILLARY THYROID-CARCINOMA - STRONG SUPPRESSION OF PEROXIDASE GENE-EXPRESSION

It is believed that qualitative changes in thyroid peroxidase (TPO) ca use decreased enzyme activity in differentiated thyroid carcinoma, To re-evaluate TPO expression in thyroid cancer, TPO mRNA expression was compared with TPO protein expression in 38 samples of thyroid tissue o btained from patients with various thyroid diseases. In Northern blot studies, while TPO mRNA was highly expressed in tissues from all 18 be nign lesions, it was strongly suppressed in 14 tumours, including 12 o ut of 12 papillary carcinomas, one of seven follicular carcinomas, and one medullary carcinoma, TPO mRNA was not detected in six carcinomas, of which four were papillary, one follicular, and one medullary, by t he usual Northern blot method, The 14 cases with strong underexpressio n of TPO mRNA were very weakly stained with anti-TPO monoclonal antibo dy 38E, whereas all 18 benign tissues mere strongly stained. Moreover, a comparative study of TPO expression by Northern blot and immunohist ochemical analysis revealed a positive correlation between TPO mRNA ex pression and the staining intensity of TPO protein. These results sugg est that strong suppression of TPO mRNA transcription causes low TPO a ctivity in papillary carcinoma; immunohistochemical loss of TPO may. b e a useful diagnostic marker, TPO mRNA expression in differentiated th yroid carcinomas did not always correlate with the mRNA expression of thyroglobulin, thyroid stimulating hormone receptor, and thyroid trans cription factor 1.