Expression of Pax-8, p53 and bcl-2 in human benign and malignant thyroid diseases

Background: Immunohistochemical expression of the transcription factor Pax- 8 in human thyroid diseases has never been investigated The relationship be tween Pax-8, bcl-2 and p53 in thyroid neoplasms is also matter of interest. Materials and Methods: Seventhy-three thyroid tissue samples were evaluate d for the expression of Pax-8, p53 and bcl-2 using the immunoperoxidase tec hnique. The series included II follicular adenomas, II goitres, 23 papillar y carcinomas 16 follicular carcinomas 6 undifferentiated carcinomas and 6 m edullary carcinomas. Results: The percentage of Pax-8 positive cell's range d from 14.9 to 27.1% and 10.1 to 39% in goitres and follicular adenomas, re spectively Among differentiated carcinomas follicular histotype showed a Pa x-8 immunoreactivity ranging from 0 to 26.5% of the neoplastic cells wherea s in papillary carcinomas the percentage of positive cells ranged from 0 to 16.8%. None out of the six undifferentiated carcinomas showed Pax-8 immuno reactivity. The same negative pattern was noticed in medullary carcinomas. A statistically significant difference in Pax-8 expression was observed bet ween non-malignant and malignant diseases (p<0.0001). A different reactivit y for Pax-8 was also noticed between differentiated carcinomas and undiffer entiated carcinomas (p=a.07). None of the benign tissues stained for p53 wh ereas among malignant specimens different percentages of p53 expression wer e observed with all undifferentiated carcinomas expressing the highest posi tivity (range 24.1-88.6%). Finally, when a combined analysis of bcl-2 and P ax-8 reactivity was carried out, some carcinomas proved to be Pax-g negativ e and bcl-2 positive whereas others showed a similar immunorenctive pattern for both Pax-8 and bcl-2. Conclusions: Pax-8 is mainly expressed in benign rather than in malignant thyroid diseases and, among neoplasms, differenti ated carcinomas express Pax-8 more frequently than undifferentiated carcino mas An inverse pattern was observed for p53. Bcl-2 seems to be partially re lated to Pax-8 expression. However, a Pax-8 independent bcl-2 expression is also evident.