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Can bioidentical hormones cause breast cancer?

Dr. Jack Merendino, MD
Endocrinology Diabetes & Metabolism
All estrogens, whether bio-identical or synthetic, increase the risk of breast cancer. As with any medical treatment, there are both risks and benefits to hormone replacement therapy (HRT). Estrogen replacement relieves hot flashes and often improves mood and sleep disturbance. Estrogens improve bone density. The major negative is probably a moderate increase in the risk of breast cancer.

An important and somewhat complicated question is the relationship of hormone replacement therapy and heart disease. A great deal of evidence indicates that estrogen should protect against the development of atherosclerosis–hardening of the arteries. On the other hand, the Women’s Health Initiative, a major study designed to determine the safety and effectiveness of HRT, indicated that estrogen therapy increased heart disease risk. A subsequent analysis of the data revealed that when HRT was started in the peri-menopause it helped protect against the development of heart disease. When initiated years after menopause, HRT increased the risk of heart disease. Many of us -- me included -- believe that this means that estrogens protect against the development of atherosclerosis. However, estrogens are well-known to increase the risk of blood clots. In a woman who has gone without hormone replacement therapy for many years after menopause atherosclerosis may have developed. In this case, the estrogen increases the likelihood that a blood clot will form in a blocked artery and cause a heart attack or similar problem. Therefore, if hormone therapy is to be used it is safest to initiate it during the peri-menopausal period.

Some people believe that “bio-identical” hormones are safer than other forms of HRT. The evidence on this is really not clear. All forms of estrogen and progesterone -- bioidentical or not -- have both risks and benefits. It is important for a woman to consider her unique, individual circumstances. If her risk of breast cancer is low but there is a strong family history of osteoporosis, or if her menopausal symptoms are severe, she may well elect to start HRT. If her family history of breast cancer is strong, she may well decide that the risk is too high to consider treatment.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.