Among the markers of thyroid origin, PAX8 was the most reliable in anaplastic carcinomas, while TTF-1 reactivity was found in only 5% of anaplastic carcinomas and thyroglobulin was always negative.
The results show that TTF-1 and Pax-8 are expressed in well differentiated adenomas and that their expression decreases in less differentiated papillary and follicular carcinomas and is lost in undifferentiated anaplastic carcinomas.