ABSTRACT
Several factors are involved in the thyroid tumourigenic process. The role of Retinoblastoma [Rb] tumor suppressor gene mutation in thyroid carcinogenesis has been discussed. In this study we investigated the expression of Retinoblastoma gene in thyroid neoplasms and its association with clinical and histological findings, to evaluate its ability in distinguishing benign and malignant thyroid neoplasms and as a prognostic factor. The present cross sectional study investigated Avidin - Biotin immunohistochemistry using the Dako Rb - 1 clone in a series of 200 formalin - fixed, paraffin - embedded thyroid lesions, including 39 benign and 161 malignant neoplasms. Nuclear immunoreactivity in more than 10% of tumor cells was assessed as positive. Rb was positive in 74.2% of follicular adenoma, 87.5% of hurthle cell adenoma, 46.2% of papillary carcinoma, 66.7% of follicular carcinoma, 29.4% of medullary carcinoma and 50% of anaplastic carcinoma. Overall Rb nuclear immunoreactivity was observed in 76.9% of benign tumors and 45.9% of malignant lesions. No significant difference in Rb expression between follicular adenoma and follicular carcinoma was seen; also no association was found between Rb expression and invasiveness in malignant tumors. The results of this study indicate that Rb gene expression in benign thyroid tumors is significantly higher than in malignant ones [P=0.001], an association observed particularly in women. Rb gene inactivation is likely to play a role in malignant evolution of thyroid neoplasms and considering female predominance in thyroid tumors, Rb immunohistochemistry can potentially aid in the distinction between benign and malignant thyroid tumors in conjunction with morphology, but it is not helpful in differentiation between follicular adenoma and follicular carcinoma