The article presents the data on the structure and mechanisms of β-сatenin functioning. The basic aspects of the role of β-сatenin in malignant transformation have been studied at various tumors. Primary structure of β-catenin allows it to interact with many factors and ligands, including transcription factors, α-catenin, cadherin, Axin, Rho family GTPases, Bcl9 et al. This interaction is the base for β-catenin's intracellular multifunctioning. The review presents data on the participation of β-catenin in the mechanisms of adhesion, regulation of RNA metabolism, formation contacts with the cytoskeleton and its role in the canonical Wnt signaling pathway, marked examples pro-inflammatory and anti-inflammatory effects of β-catenin. The β-catenin involvement in malignant transformation and progression of certain tumors is not in doubt. The data on the changes in β-catenin expression in the given examples of colon cancer, prostate cancer, different forms of thyroid cancer and hepatocellular carcinoma are presented with the prospects of its use as a marker and a predictor of malignant transformation. Continued research in this area will not only make use of β-catenin as a potential predictor of malignant tumors, but also to develop approaches to targeted therapy.

The ever increasing incidence of thyroid cancer throughout the world poses the problem of differential diagnosis of thyroid nodules at various stages of their formation. Objective: to determine the most important clinical, laboratory and instrumental parameters of thyroid nodules for the assessment of their malignancy potential and to identify "defects" of clinical and instrumental examination of patients with nodular goiter in clinical practice. Materials and methods: we analyzed the data of general clinical research, hormonal profile, and thyroid ultrasound studies performed on the basis of various clinics in the city of Tomsk (41%), Endocrinology Department of the OGAUZ TOKB consultative and diagnostic polyclinic (28 %), and Cancer Research Institute (31%) for the period from 2012 to 2014. The patients were selected for surgery. Pre-operative data were compared with histological features of the nodules. Results: we analyzed «defects» of patient examination, statistical data on clinical and laboratory-instrumental parameters of thyroid nodules. Conclusion: «defects» of description of ultrasound data significantly reduce sensitivity of the method for predicting malignancy of thyroid nodules. The description of the material obtained by US-FNA alone, in the absence of the conclusion of medical cytologists, has no informative value. Low specificity of a cytological study (48.4%) and its high sensitivity (95.8%) suggests overdiagnosis of thyroid cancer.

We compared the results of gene molecular and immunocytochemical studies of β-catenin and E-cadherin in different variants of nodular thyroid disease (nodular colloid goiter, follicular thyroid adenocarcinoma, papillary thyroid cancer) and revealed changes of the function of the E-cadherin/β-catenin complex leading to switching from adhesion function of β-catenin in nodular colloid goiter to predominantly transcriptional activity in papillary carcinoma. The results confirm the important role of disturbances in E-cadherin-β-catenin interactions in the mechanisms of malignant transformation of follicular epithelium.