The word “estrogen” actually refers to a family of related molecules that stimulate the development and maintenance of female characteristics and sexual reproduction. The most prevalent forms of human estrogen are estradiol and estrone. Both are produced and secreted by the ovaries although estrone is also made in the adrenal glands and other organs. Estriol is a third form of estrogen that is produced by the placenta and is only synthesized in significant amounts during pregnancy.
The breast and the uterus, which play central roles in sexual reproduction, are two of the main targets of estrogen. The estrogens normally promote healthy cell growth in the breast and uterus. Yet, this same propensity to stimulate cell proliferation can also increase the risk of developing breast or uterine cancer.
The apparent connection between breast cancer and estrogen has been noted for over a century, beginning with the publication of a paper in 1896 by Scottish physician George Beatson. The article, which appeared in the British medical journal, The Lancet, reviewed the case of a 34-year-old woman with advanced breast cancer who lived for four years after her ovaries were removed, a treatment now known as ovarian ablation.
Breast cancer risk increases with menstruation at an early age, late age at menopause, later age at first full-term pregnancy, and few or no pregnancies. Research suggests that the reason may be that these situations result in longer lifetime exposure to estrogen, which promotes cell division in breast tissue and possibly unregulated cell growth, leading to mutations.
BODY FAT & ESTROGEN
According to some studies, body fat and menopause appear to be important factors in the estrogen-cancer connection. Obesity has a complex relationship to breast-cancer risk that differs depending upon menopausal status. In one study published in the International Journal of Cancer, which included 176,886 European women between 18 and 80 years of age, researchers found a 65 percent increase in the risk of breast cancer for
After menopause, the adrenal glands continue to produce small amounts of a steroid called androstenedione, which is converted into estrogens by aromatase in fat tissue. Increased levels of this steroid may be the reason why menopause and obesity are associated with higher estrogen levels and increased risk of breast cancer. It is also believed that excess fat may cause the body to produce more estrogen than is necessary for normal cell growth.
In addition, fat cells secrete the pro-inflammatory chemicals, TNF-alpha and IL-6, either of which can act to increase the production of aromatase, which is directly related to increases in estrogen. Obesity is also associated with greater tumor burden in women diagnosed with breast cancer, higher-grade tumors, and poorer prognosis and/or increased mortality. Weight gain and obesity have been identified as the most important risk and prognostic factors for breast cancer in postmenopausal women. Moreover, the association between obesity and cancer has also been established for colorectal and prostate cancer.