Thyroid disease in relation to breast cancer

Abstract

A controversy exists in regard to thyroid function and breast cancer. Hypothyroidism has been suggested as being either protective from breast cancer or predisposing to the disease. It has been hypothesized that a deficiency in circulating thyroid hormones may hypersensitize the mammary glandular epithelium toward prolactin and estrogens, thus aiding the development of breast neoplasia. On the other hand, thyroid hormone replacement therapy has been connected with an increased risk of breast cancer, but this has been contested. At this time the American Thyroid Association recommends that, if indicated, hypothyroid patients should take their thyroid hormone medication. Hyperthyroidism has been associated with a decreased risk of breast cancer. Also, in hyperthyroid patients with inoperable breast cancer, the malignant growth is thought to be slowed. However, this, too has been disputed. Moreover, hyperthyroidism has been connected with the development of breast cancer in premenopausal women. At present no role of thyroid hormone in the pathobiology of breast cancer can be defined. It seems that the "thyroid-breast cancer controversy" can only be resolved by a prospective study preferably on postmenopausal women correlating thyroid (T3, T4, PBI), pituitary (TSH, TRH, Prolactin), and adrenocortical (androgens) function tests with the clinical examination of thyroid, breast, and genital apparatus and determination of the estrogen status (vaginal smear, plasma estrogens) as well.

Breast Cancer Risk in Postmenopausal Women with Medical History of Thyroid Disorder in the Women's Health Initiative

“…A hypothyroid state reduced the size and proliferation of malignant breast tumors and increased tumor necrosis in vitro, but the tumors exhibited a higher metastatic occurrence (17,37). It has been suggested that hypothyroidism leads to hypersensitization of mammary glandular epithelium to estrogen and prolactin secondary to abnormally low circulating thyroid hormone (38). It has also been hypothesized that there is a genetic predisposition for both hypothyroidism and breast cancer (14).…”

MECHANISMS IN ENDOCRINOLOGY: Primary HT and risk for breast cancer: a systematic review and meta-analysis

“…TR gene transcription deregulation has been implicated in breast carcinogenesis (19) and TR-a receptors have been shown to translocate from the nucleus to the cytoplasm of breast cancer cells, suggesting a possible role in the histological changes of the epithelium during carcinogenesis (20). It has been shown that hypothyroidism may result in hypersensitization of the mammary glandular epithelium to prolactin and estrogen, thus promoting breast cancer growth (21). Moreover, estrogens as well as pregnancy increase thyroxinebinding globulin concentration that in turns increases serum concentration of total thyroxine (T 4 ), with a transient reduction of free T 4 , and an increase of thyrotropin (TSH) (22,23).…”

Thyroid hormone levels in human breast cyst fluid

“…Throughout the years the problem of the relation¬ ship of thyroid function to breast disease has been the subject of considerable controversy. Both hypoand hyperthyroidism have been claimed to repre¬ sent factors that predispose to or protect from breast malignancy (Bogardus & Finley 1961;Moosa et al 1973;Vorherr 1978). However, more recent studies (Hedley et al 1981;Kalache et al 1982) have failed to provide evidence that the occurrence of breast cancer is influenced by the thyroid hor¬ mone action.…”