COMPARISON OF THYROID PEROXIDASE EXPRESSION WITH CELLULAR PROLIFERATION IN THYROID FOLLICULAR TUMORS

Thyroid cancer is associated with abnormal thyroid peroxidase (TPO) ex pression as shown by abolition of immunodetection by monoclonal antibo dy 47 (Mab 47),. The purpose of this study was to determine the relati on of this abnormality with differentiation and proliferative potentia l of follicular tumors evaluated by analyzing thyroglobulin (TG) expre ssion and proliferative cell nuclear antigen (PCNA) index. TPO, TG, an d PCNA immunostaining were performed in a series of 30 thyroid follicu lar tumors ranging from adenoma to invasive carcinoma. Our findings co nfirmed that TPO abnormalities and PCNA index were correlated with mal ignancy, and that PCNA as well as TPO could be used to determine the g rowth potential of follicular proliferations in fine-needle aspirates. The most discriminant parameter was the ratio between the percentage of Mab-47 and PCNA positive cells. Ratios under 0.6 were correlated wi th malignancy in 90% of the cases, with only 3 cases of atypical adeno mas being misdiagnosed as carcinomas. An inverse correlation was found between TPO and PCNA expression, but TC, which persisted at high leve ls in several actively growing follicular carcinomas, did not appear d irectly linked to cellular proliferation. These findings confirm that, unlike a decrease in TG synthesis that merely reflects the progressiv e loss of differentiation occurring in high-grade proliferations, alte ration of TPO is an early marker of thyroid follicular tumors, closely related to acceleration of tumor growth in the first stages of malign ant transformation.