HIDDEN RADIOIODINE-SENSITIVE AND RADIOIODINE-RESISTANT METASTASES OF PAPILLARY THYROID CARCINOMA: CLINICAL ASPECTS

Abstract

Background. The resistance of metastases to radioiodine is a significant clinical problem during targeted radioiodine therapy in patients who underwent thyroidectomy for papillary thyroid carcinoma (PTC). The existence of hidden lymph nodes that are affected by PTC metastases, especially if they are radioiodine-resistant (RIR), doubles the problem, because it poses a threat of further widespread metastasis of carcinomas, the occurrence of relapses after surgical treatment, low effectiveness of radioiodine treatment.

Purpose. To analyze a number of clinical and oncological characteristics of the disease, which could, to a certain extent, predict the presence of radioiodine-resistant metastases in patients whose tumors, based on the results of preoperative diagnostics, had the status N0.

Materials and methods. Cohort study of the frequency of metastases in the neck lymph nodes of patients of three groups – without metastases, with radioiodine-sensitive (RIS) metastases and RIR metastases – depending on a number of clinical parameters (age and sex of patients, tumor size and its invasive characteristics, presence of concomitant autoimmune thyroiditis). The proportion of affected lymph nodes to the number of removed ones was determined. Statistical data processing was performed using the Pearson's χ² distribution consistency criterion, as well as the Student's test.

Results. Age and gender characteristics of the patients are not associated with the prognosis of the existence of RIR metastases of PTC, although the trend towards a larger size of tumors whose metastases were RIR was observed in the group of women, but not in men. The size of the carcinomas is associated with an increase in the frequency of RIR metastases only in the case of tumors that do not go beyond the thyroid gland and whose diameter does not exceed 4 cm (categories T1-T2). The lowest frequency of RIR metastases compared to the frequency of RIS ones was observed for tumors of category T1a, the highest – for PTC of category T2. They did not reveal the relationship between the frequency of RIR metastases and such characteristics of PTC as invasion into the tumor capsule, intrathyroidal or extrathyroidal invasion, as well as multifocal growth of tumor cells, although the frequency of tumors with both RIR and RIS metastases was higher compared to that of invasive carcinomas, which did not metastasize. A clear connection between the frequency of RIR metastases and the presence of thyroiditis in patients has been established: in the association of an autoimmune disease with PTC, RIR metastases occurs much less often. The proportion of metastatic lymph nodes was the highest among the removed lymph nodes of the central compartment.

Conclusions. The frequency of radioiodine-resistant metastases of the papillary thyroid carcinoma in patients with preoperative tumor status N0 does not depend on the age of the patients, their gender, as well as the invasive characteristics of the tumors. Rarely, hidden radioiodine-resistant metastases occur in patients with microcarcinoma and against the background of papillary thyroid carcinoma-associated autoimmune thyroiditis. Determining the proportion of metastatic lymph nodes among all those removed during lymph node dissection can be useful for predicting recurrence of the disease in the postoperative period.