Hormones and Breast Cancer: New Information from the Women's Health Initiative Study

Dr. Nicholas LeRoy, DC, MS

Researchers have recently published in the Journal of the American Medical Association the results of ongoing tracking of women that were part of the Women's Health Initiative study (WHI). Released in October 2010, this placebo-controlled study found that women who were taking Prempro, an estrogen/progestin combination therapy taken postmenopausally, experienced a greater breast cancer incidence, and the cancers were more commonly lymph node-positive.

The WHI was launched in 1991 and consisted of a set of clinical trials and an observational study, which together involved 161,808 generally healthy postmenopausal women. The clinical trials were designed to test the effects of postmenopausal hormone therapy, diet modification, and calcium and vitamin D supplements on heart disease, fractures, and breast and colorectal cancer.

The hormone trial had two studies: the estrogen-plus-progestin study of women with a uterus and the estrogen-alone study of women without a uterus. (Women with a uterus were given progestin in combination with estrogen, a practice known to prevent endometrial cancer.) In both hormone therapy studies, women were randomly assigned to either the hormone medication being studied or to placebo. Those studies have now ended. The women in these studies are now participating in a follow-up phase, which lasted until this year.

With the latest release of hormone trial data, doctors and women alike are being forced once again to re-evaluate the safety of hormone replacement therapy and when its use is justifiable. In other words, to determine the risk versus benefit on an individual basis. Before discussing who may benefit by hormone therapy, I am compelled to address some specifics of this study and their possible significance.

This hormone trial used a synthetic estrogen combined with a synthetic progesterone known as a "progestin". Progestins are the result of pharmaceutical manufacturers modifying progesterone so that it could be patented. There has been research suggesting that synthetic estrogens, and even more so progestins, have deleterious effects in humans that may not be matched by naturally occurring hormones. Prior research has demonstrated that progestins may be the real culprit that increases breast cancer risk as well as other side effects of synthetic hormone replacement therapy.

The risk of using this combination of hormone replacement therapy, in addition to increasing the incidence and severity of breast cancer, is increased risk of heart disease, stroke and blood clots in the lungs. The potential benefits are improvement in bone density, mood, sleep and additional symptoms of menopause including weight gain, decreased libido and vaginal dryness.

It is my recommendation that women discuss the risk versus benefits of hormone therapy with their doctor. If menopausal symptoms are severe, and a family history of breast cancer is lacking, a short use--less than several years of hormones--may outweigh the risks. I likewise recommend a healthy diet, supplementing with vitamin D, and maintaining a healthy weight (studies have demonstrated amount of body fat is a significant risk factor for breast cancer). If menopausal symptoms are not severe and/or a woman has a family history of breast cancer, the risk may outweigh the benefit. I also recommend that if an educated decision has been made to use hormones, natural hormones are probably a better decision than the synthetic hormones.

"Bioidentical hormone therapy" has been introduced as a means to diminish post-menopausal symptoms without increasing the adverse effects associated with synthetic replacement. However reasonable this may seem, it is at this point unknown to what degree bioidentical hormones contribute to breast cancer. There are simply too few studies that have examined any correlation despite the fact that naturally occurring hormones have been used as an alternative to traditional pharmaceutical preparations for over a decade.

Because a woman's own estrogen and progesterone (it doesn't get any more bioidentical than this!) are known to increase susceptibility to breast cancer, I likewise advise caution when considering the use of "natural" hormones. However, it seems reasonable that the risk associated with natural hormone therapy will be found to be safer than their synthetic counterpart.

In summary, the JAMA publication of Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women is yet one more warning of the risk of using reproductive hormones to ameliorate menopausal symptoms and caution is advised for women considering the use of bioidentical hormones and especially synthetic hormone replacement therapy.