TSH and Thyroid Hormones’ Influence on Thyroid Cancer Development

Thyroid cancer (TC) is the most common type of endocrine malignancy. Moreover, spreading of this pathology still actively continues. According to the American Thyroid Association's recommendations, the diagnosis of thyroid nodal nodes requires assessment of thyroid stimulating hormone level (TSH), which is one of the most powerful stimulators for follicular cells proliferation. According to scientific data, high TSH level is associated with an increased risk of thyroid cancer developing. There is also evidence that an increase in TSH levels is associated with the progression of tumor growth. On the other hand, from the perspective of fundamental principles of hypothalamic-pituitary-thyroid axis regulation, an increased TSH level could be connected with a decrease in the thyroid hormones level. However, in the official literature sources there is no scientific justification of the thyroid hypofunction and TC development relation. Thus, the purpose of the study was to evaluate the functional state of the thyroid gland and determine the informative criteria associated with thyroid cancer development and progression. A retrospective analysis of the thyroid's functional state in 590 patients with thyroid cancer and 40 patients with follicular adenomas was conducted to assess the informative value of the hormonal indices associated with malignant tumor growth. Evaluation of the functional state of the thyroid gland was carried out according to the serum levels of thyroid stimulating hormone, free thyroxine (fT4) and free triiodothyronine (fT3). The impact of such confindings as gender, age, multifocality of growth, concurred Hashimotos thyroiditis was considered. It was found out that in most patients with thyroid cancer the serum TSH, FT3 and FT4 concentration was within the normal range. TSH, fT3 and fT4 levels were not dependent on histological type of tumor, age and tumor size. However, TSH was associated with sex, the presence of concomitant autoimmune thyroiditis and multifocal growth of tumors. No significant differences in thyroid hormones levels between patients with benign and malignant tumors had been found, however, TSH level was higher among patients with thyroid carcinoma (P=0.022). It should be noted, that among 590 patients with thyroid cancer, only 26 individuals (4.7%) had high TSH level (more than 4 mkIU/ml). Moreover about 80% of patients with PTC demonstrated TSH level lower than 2.5 mkIU/ml. Assessment of TSH and tumor invasiveness did not reveal a significant association of TSH with the risk of metastases and extrathyroid invasion. The risk of metastasis of papillary thyroid carcinoma was related to sex (P = 0.0002). In addition, there was a significant association between TSH level and the concurred Hashimoto's thyroiditis (p <0.0001), as well as between Hashimoto thyroiditis and female (P<0.0001). In addition, strong connection was found between TSH serum and multifocality of tumor growth (P = 0,049). Thus, the relationship between TSH serum level and tumor growth characteristics, such as tumor size, extrathyroid invasion, metastasis to lymph nodes, was not revealed in the study. However, TSH was associated with sex, the presence of concurred autoimmune thyroiditis and multifocal growth of tumors.