Аннотация:One of the cancer prevention measures involves the correctionof the altered functions of the body’s regulatory systems. Manymalignant tumors are accompanied by the thyroid system dysfunction.The aim of our study was to reveal an effect of an iodine-containing drug on the development of a tumor process in thelungs and the level of thyroid hormones in blood and the thyroid gland in male rats.Material and methods. Outbred white male rats were divided into the following groups: a group of intact animals (n=7); acomparison group – 5 weeks after an intravenous inoculationof sarcoma 45 (S45) at 2*106 (n=7); a main group – 5 weeks after an intravenous inoculation of S45 and intragastric administration of Stellanin at a single dose of 0.4 mg/kg within an hourafter the inoculation (n=10). RIA was used to determine levels offree (F) and total triiodothyronine (T3) and thyroxine (T4) in theblood serum and the thyroid.Results. The lungs of rats in the comparison group were totally affected by the tumor, and the thyroid gland showed asharp decrease in the levels of all hormone forms: T4 – by 18.7times, T3 – by 8.5 times, FТ4 – by 8.1 times, FТ3 – by 21.3 times,while only FТ4 and FТ3 decreased in blood by 2.5 and 1.5 times,respectively (p<0.05). No tumor lesions were detected in thelungs of rats of the main group, and the hormone levels exceeded the levels in the comparison group: in the thyroid, FT4by 3.7, T4 by 15.0 and T3 by 6.0 times; in blood, FT4 by 3.3 andFT3 by 1.7 times.Conclusions. The effect of Stellanin inhibiting malignantgrowth of S45 in the lungs is accompanied by the restoration oflow levels of thyroid hormones in the thyroid and blood.