[Immunohistochemical study in differential diagnosis of benign and malignant lesions of the thyroid gland].

The paper is devoted to immunohistochemical (IHC) investigation of various benign and malignant proliferating lesions in the thyroid with a special focus on borderline lesions--atypical adenomas (AA) and focal adenomatous areas (FAA). All papillary carcinomas (PC) and FAA in Hashimoto thyroiditis demonstrated strong immunoreactivity for CK-19. More than 50% of PCNA-positive cells were detected in most of the investigated carcinomas; in FAA, and in AA PCNA expression was not so prominent but higher than in other adenomas and nodular goiters. Strong expression of vimentin by follicular epithelium was detected in PC. In FC, AA and FAA it was focal from moderate to strong. In other cases immunoreactivity to vimentin was weak or absent. Thus, it is worth to form on the basis of histological and IHC results the group of thyroid proliferating processes with possible malignant transformation. AA and FAA with more than 10% PCNA-immunoreactive cells and vimentin expression from moderate to strong should be included in this group. Further observation of our patients will enable to assess malignant potential of this processes. Besides, CK-19 expression is an additional criterion for the diagnosis of early PC.