EXPRESSION OF P21 (WAF1 CIP1) PROTEIN IN CLINICAL THYROID TISSUES/

p21 (WAF1/CIP1) protein expression in various thyroid tissues, includi ng thyroid carcinoma, was studied by means of immunohistochemistry usi ng anti-p21 monoclonal antibody. Normal follicles and hyperplasias rar ely expressed p21, whereas immunohistochemically positive cells were a lso too rarely found in follicular adenomas to justify these cases bei ng classified as positive. Twenty eight of the 93 carcinomas examined (30.1%), however, were positive for p21. Of the p21-positive cases, 80 % of the undifferentiated and 28.6% of the poorly differentiated carci nomas showed lesions co-expressing p21 and p53. If diffuse immunoreact ivity of p53 reflects the p53 mutation, our results indicate that p21 in these carcinomas can be induced by p53-independent as well as by p5 3-dependent pathways. On the other hand, well-differentiated carcinoma s did not co-express these two proteins and it therefore remains uncle ar whether p53-independent or p53-dependent pathways are predominant i n this type of carcinoma. The incidence of expression of p21 was very similar in undifferentiated (26.3%), poorly (28.0%) and well-different iated carcinomas (32.7%), even though they are characterised by differ ent degrees of malignancy. Furthermore, no correlation between p21 exp ression and either clinical parameters or patient's prognosis could be established. These results suggest that p21 is only marginally relate d to the characteristics of thyroid carcinoma and can play only an adj uvant role in regulating the progression of this carcinoma.