Y. Ito et al., EXPRESSION OF THE RETINOBLASTOMA GENE-PRODUCT IN CLINICAL THYROID TISSUES - A REASON FOR THE SLOW GROWTH OF THYROID-CARCINOMA, Oncology Reports, 3(1), 1996, pp. 57-62
We investigated the expression of the retinoblastoma gene product (pRB
) in various clinical thyroid tissues. Follicular cells in the normal
thyroid sometimes expressed pRB but their positive cell ratio was alwa
ys less than 10% as it was in hyperplasia. All of the 57 carcinomas te
sted expressed pRB immunohistochemically with various positivity and 3
6 of them (63.2%) showed high immunoreactivity. In contrast, only four
of the 15 follicular adenoma samples (26.7%) revealed moderate pRB im
munoreactivity and there was a statistically significant difference (p
<0.01) in PRE positivity between the carcinomas, including follicular
ones, and benign follicular adenomas. These findings indicate that pRB
may be closely related to the suppression of tumoral growth, especial
ly of carcinoma growth of the thyroid. Western blot analysis showed pR
B immunoreactivity for all tested samples to be a single, sharp band l
ocated at 110 kDa, indicating that pRB in thyroid tumors is always unp
hosphorylated and active. The present study suggests that frequent pRB
expression in an active form could be one of the reasons for the slow
growth and excellent prognosis of thyroid carcinoma.