[Differential criteria between papillary and follicular thyroid carcinoma--initial conclusions from a multicenter...

Histopathological diagnosis of thyroid cancer is difficult and requires much experience. Pathologists have to know many histopathological variants and be aware of the current diagnostic criteria. The aim of the study was to unify criteria applied all over the country and compare whether the accuracy of diagnosis has changed in the course of the last fifteen years. In a multicenter trial, 36 pathologists from 25 centers reevaluated 232 thyroid tumors operated between 1985-1998. The reference diagnosis was given on the basis of evaluation made by four experienced pathologists. The two-step analysis was performed. At first, the accuracy of the diagnosis of malignant neoplasm was evaluated. Then, the accuracy of the diagnosis of the cancer histotype was analyzed, with estimation of kappa coefficients and their asymptomatic standard error. Comparison of primary and reference diagnoses revealed statistically significant differences--in 17% of cases the primary diagnosis of cancer was not confirmed by experienced pathologists. Kappa coefficient for the diagnosis of cancer histotype was 0.53 + 0.06. On the contrary, the diagnoses made by the participants of the trial did not differ significantly from the reference ones. Kappa coefficient for the diagnosis of cancer histotype was significantly higher than for primary diagnoses with 0.63 +/- 0.10 (p < 0.001). The first results of the multicenter trial indicated that the most frequent diagnostic error made at primary diagnosis was the overdiagnosis of follicular thyroid carcinoma. Thus, a summary of strict criteria for papillary and follicular thyroid carcinoma is also given.