Insulin resistance and hyperinsulinemia as pathophysiological links between thyroid cancer and obesity. Review

In recent decades, there has been a marked increase in the prevalence of thyroid cancer. The incidence of well‑differentiated thyroid cancer (TC) has been increasing dramatically over the last 20 years worldwide, and TC is expected to be the fourth most common cancer by 2030. The rapid increase in the detection rate of TC in recent years has caused many changes in the management of these malignancies. TC accounts for 3.4% of all cancers diagnosed annually worldwide. Some data suggest that TC is increasing globally much faster than other malignant lesions. This might be a consequence of the widespread use of ultrasonography (US) examination and ultrasound guided fine needle aspiration biopsy (UG‑FNAB) procedures. Generally, this observation led to a globally highlighted discussion about the causes of such a situation. Some authors say that the higher incidence of TC is due to overdiagnosis. Others believe that various additional factors may play a role in this observation, such as obesity and an increased exposure to ionizing radiation. This phenomenon has paralleled the increase in the prevalence of obesity worldwide, which is associated with insulin resistance. Associations between these entities have been hypothesized, mainly for older and female populations, but they remain unclear. The aim of this review article was to systematically review the literature in an attempt to determine whether the increase in the prevalence of thyroid cancer is due to obesity or due only to improved detection with the better imaging techniques available. A thorough literature search on PubMed and application of selection criteria identified 14 appropriate studies. The detailed analysis of the data from these studies indicated that there is a suggestive association between thyroid cancer, obesity, insulin resistance and hyperinsulinemia for both genders. Therefore, the increased prevalence of thyroid cancer is not dependent on improved detection only. Further research should be performed for complete understanding of the pathophysiological associations, especially regarding adipose tissue and genetics, but also for the improvement of preventive public health policies.