Triiodothyronine and breast cancer

Abstract

The thyroid hormones (THs), triiodothyronine (T3) and thyroxine (T4), are essential for survival; they are involved in the processes of development, growth, and metabolism. In addition to hyperthyroidism or hypothyroidism, THs are involved in other diseases. The role of THs in the development and differentiation of mammary epithelium is well established; however, their specific role in the pathogenesis of breast cancer (BC) is controversial. Steroid hormones affect many human cancers and the abnormal responsiveness of the mammary epithelial cells to estradiol (E2) in particular is known to be an important cause for the development and progression of BC. The proliferative effect of T3 has been demonstrated in various types of cancer. In BC cell lines, T3 may foster the conditions for tumor proliferation and increase the effect of cell proliferation by E2; thus, T3 may play a role in the development and progression of BC. Studies show that T3 has effects similar to E2 in BC cell lines. Despite controversy regarding the relationship between thyroid disturbances and the incidence of BC, studies show that thyroid status may influence the development of tumor, proliferation and metastasis.

Keywords: Thyroid hormone; Triiodothyronine; Breast cancer; Mammary gland and metabolism

Core tip: Breast cancer (BC) is a malignant tumor occurring much more frequently in women than in men; worldwide, the incidence of BC has increased markedly in recent years. It is estimated that 1.7 million women will be diagnosed with BC in 2020, marking an increase of 26%, compared to the current incidence: 1.35 million new cases annually. Countless environmental risk factors, pathological conditions, and physiological agents, as well as thyroid hormones (THs), have been involved in the development of BC. Various lines of evidence suggest tumor-promoting effects of THs. The literature contains controversial reports regarding the relationship between thyroid diseases and BC; furthermore, studies reporting both an excess of and a lack of THs may affect breast development and progression to cancer. Epidemiologically, many studies suggest that hyperthyroidism is a factor in the development of BC. Furthermore, experimental studies have shown that high levels of THs reduce the interval of multiplication of BC cell lines. Therefore, the influence of THs on BC is unclear. However, the majority of BC research suggests a relationship, primarily, when the molecular aspects of these hormones are considered in the progression of this type of tumor.