Immunohistochemical analysis of expression of bcl-2 protein in papillary carcinomas and papillary microcarcinomas of the thyroid gland.

AIM To compare the expression of anti-apoptotic protein bcl-2 and tissue proliferation Ki-67 antigen in tissues of human papillary thyroid carcinoma (PTC) and papillary thyroid microcarcinoma (PTMC). METHODS Bcl-2 protein expression in PTC and PTMC has been evaluated by immunohistochemical analysis. RESULTS Bcl-2 protein was observed in normal thyroid gland in all the cases; in 25% of the cases of papillary carcinomas the immunoreaction was strong and in 75% of the cases--moderate. In 25% of the cases of papillary microcarcinomas the bcl-2 expression was totally negative and 35% was moderate. Bcl-2 expression was lower in non-sclerosing non-encapsulated (NSNE) (25%) cases of PMCs than in non-sclerosing encapsulated (NSE) (57.15%) cases of PTMCs (p < 0.05). MIB-1/Ki-67 expression was notably reduced or not expressed in normal and benign thyroid tissue. MIB-1 immunoreactivity was present in papillary carcinoma, and on a lower level--in PTMCs. The MIB-1 labelling index of NSE and sclerosing non-encapsulated (SNE) cases was lower than that in NSNE (p < 0.005). CONCLUSION The present study indicated that NSNE cases of PTMCs may be an early stage in tumor progression, and the bcl-2 and MIB-1 immunohistochemistry may be a valuable tool in predicting the malignant behavior in PMTCs, and contributes to the understanding the growth characteristics of papillary carcinomas of the thyroid gland.