An Immunohistochemical Analysis of Cyclin D1, p53, and p21waf1/cip1 Proteins in Tumors Originating fromthe Follicular Epithelium of the Thyroid Gland*

Summary This study aimed at clarifying the factors closely related to the tumor progression of thyroid neoplasms. We examined the immunoreactivity of cyclin D1, p53, and p21 waf1/cip1 proteins in 179 thyroid tumors originating from the follicular epithelium using an immunohistochemical technique. Cyclin D1 positivity was frequent in well-differentiated thyroid carcinomas (39/122 cases), but it was rarely seen in follicular adenomas (1/33 cases), (p wafl/cip1 positivity was more frequent in well-differentiated thyroid carcinomas (43/122 cases) than in follicular adenomas (4/33 cases) (p waf1/cip1 expression in poorly differentiated carcinomas (6/7 cases). Three cases examined showed co-positivity of p53 and p21 waf1/cip1 . Our results suggest that cyclin D1 is invoved in thyroid oncogenesis. Moreover, p53 might be closely related to the development of poorly differentiated carcinomas and undifferentiated carcinomas originating from well-differentiated carcinomas.