Clinical and morphological features and unsolved issues in diagnosis of aggressive forms of papillary thyroid carcinoma

Differentiated thyroid cancer (DTC) is a disease with a favorable clinical course and high survival rate compared to other epithelial tumors. The majority of DTC (up to 85 %) is represented by various subtypes of papillary thyroid cancer (PTC). Aggressive forms of PTC characterized by early lymphogenous and hematogenous metastasis, low avidity to radioiodine therapy (RIT), low relapse-free survival rates and high mortality rate compared to other types of PTC occur among them. Preoperative diagnosis of PTC is based on the results of ultrasound (US) examination and fine-needle aspiration biopsy (FNA) with cytological examination of the aspirate. At the same time, the capabilities of cytological examination in determining the histological type of PTC are limited and it does not allow to predict its aggressiveness and plan adequate treatment. Molecular genetic tests of the tumor cytological and morphological material are effective in prognosis of aggressiveness of PTC due to the determination of specific mutations in the BRAF, TERT, RAS genes and the quantitative expression of oncogenic and tumor suppressive microRNAs. Some of these indicators are already used in the morphological classification of tumors of the endocrine system. At the same time, there are contradictory data concerning the connection of the molecular genetic portrait of PTC, the clinical manifestations of its aggressiveness (extrathyroidal invasion, early metastasis, and radioiodine resistance) and its pathomorphological structure. We tried to summarize and analyze the literature data regarding the diagnosis of aggressive variants of PTC.