thyronines and Breast-Neoplasms

Hypothyroidism and low iodine intake may be important aetiological factors in oestrogen dependent tumours of the breast, uterus and ovary. They are preventable risk factors. Iodine supplementation will hopefully lead to a decreased incidence of these cancers in future generations. The present author proposes that the tyrosyl residue in the hydrophobic oestrogen binding site of the oestrogen receptor is post translationally modified to monoiodotyrosine and hence 3,3' di-iodothyronine monoamine (T2) by peroxidase activity. He has previously proposed that various monoamine receptors are also T2 based. The densities of these receptors are increased in hypothyroidism and they exert control over release of prolactin and other hormones, including melatonin at multiple sites in the hypothalamic--pituitary axis. Melatonin is a metabolite of serotonin and hence melatonin receptors may be T2 or rT3 based as well. These factors could be significant in the aetiology of breast cancer as high prolactin and melatonin levels may be protective. Oestrogen receptor density may be increased in hypothyroidism as is certain monoamine receptor density. This would amplify the effect of high circulation oestrogen levels in hypothyroidism and may help explain why hypothyroidism and low iodine intake are risk factors for breast, uterine and ovarian cancer.

Topics: Breast Neoplasms; Diiodothyronines; Dopamine; Female; Humans; Hypothyroidism; Iodine; Melatonin; Models, Biological; Prolactin; Receptors, Estrogen; Thyronines

Plasma triiodothyronine (T3), reverse T3 (rT3), thyroxine (T4), total thyroid hormone-binding globulin (TBG) capacity, and serum albumin were assayed in patients with early and advanced breast and colonic cancer and in healthy women. Plasma T3 levels were reduced in both breast cancer group, but were reduced only in colonic cancer patients with systemic metastases. Plasma rT3 was normal in early cancer, but increased in nine of 38 (24%) with advanced breast cancer and four of 17 (24%) with metastatic colonic cancer; in consequence their rT3/T3 ratios were elevated. Plasma T4 concentrations were normal in all patient groups. Plasma TBG capacity was reduced in breast cancer patients with systemic metastases and a similar tendency occurred in metastatic colonic cancer. Levels of TBG were positively correlated with the serum albumin values. These changes were associated particularly with liver metastases.

Topics: Adult; Breast Neoplasms; Carcinoma; Colonic Neoplasms; Female; Humans; Liver Neoplasms; Middle Aged; Thyronines; Thyroxine; Thyroxine-Binding Proteins; Triiodothyronine