Well-differentiated thyroid tumors may sometimes cause diagnostic uncertainty due to difficulties in the evaluation of certain morphological criteria (capsular and/or vascular invasion, cytomorphological features). Therefore, various diagnostic/prognostic markers are currently studied, namely the markers of tumor proliferation. The aim of our study was to evaluate the proliferative MIB-1 index in 155 thyroid tumors, and to correlate it with morphological diagnosis, size of the tumors, and the patients’ age. Oncocytic tumors were represented by 59 follicular adenomas, 27 follicular carcinomas and 12 papillocarcinomas. Nononcocytic tumors comprised 24 follicular adenomas and 33 conventional papillary carcinomas. The Ki-67 antigen (formalin resistant epitope MIB-1) was detected immunohistochemically and the proliferative index (PI) of tumors was evaluated. The results were statistically analyzed using analysis of variance (ANOVA) and Wilcoxon tests (significance level p<0.05). Carcinomas showed significantly higher PI than adenomas. Moreover, PI in oncocytic adenomas was higher than in nononcocytic ones. However, proliferative activity in all types of the carcinomas was similar. The higher rates of proliferation correlated with the advanced age of the patients with follicular carcinomas (p<0.0016).

        Key words: thyroid gland - tumor - oncocytes - MIB-1 - proliferation