PROGESTERONE vs. PROGESTIN: The choice may affect your risk of breast cancer.

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Progesterone is a naturally occurring hormone in women. In the 1970’s, following a surge in the use of Conjugated Equine Estrogens to treat symptoms of menopause, there was a corresponding rise in the incidence of endometrial cancer (cancer of the lining of the uterus).  It was found that by adding progesterone to estrogen therapy, endometrial cancer could be prevented. However, in the 1970’s, progesterone was not available in a form that was well absorbed orally or transdermally, so pharmaceutical manufacturers developed and patented the first synthetic progestin (progesterone derivative), medroxyprogesterone acetate. Later, micronized progesterone was developed and the small particle size facilitates better absorption, so now, women can receive progesterone instead of a synthetic progestin as part of their hormone therapy. While both progesterone and synthetic progestins protect the endometrium, most literature demonstrates physiological differences in their effect on breast tissue. Also, studies have shown that women prefer progesterone to synthetic progestins, and report fewer side effects with progesterone.

In addition, there are physiologic differences between synthetic (non-bio-identical) progestins and “natural” bio-identical progesterone. For example:
• induces breast cancer cell apoptosis (death of cancer cell).
• inhibits estrogen-stimulated proliferation of breast epithelial cells, which can reduce the risk of breast cancer.
• has receptors in many vital areas of the body, and has beneficial effects on the heart, brain and bone, so is also needed by women who have had a hysterectomy (ie, progesterone has many other purposes besides decreasing the risk of endometrial cancer).

• are antiapoptotic, which means they do not cause cancer cells to die. 
• may significantly increase estrogen-stimulated breast cell proliferation, which can contribute to the development of breast cancer.

In a study of over 80,000 postmenopausal women, the following breast cancer risk was observed:
Women who used estrogen only were found to have a 29% increased risk of breast cancer compared to women who had never used Hormone Replacement Therapy (HRT)
Women who used estrogen plus a synthetic progestin were found to have a 69% increased risk of breast cancer compared to women who had never used HRT
Women who used estrogen plus progesterone were found to have no increased risk for breast cancer 
   “These findings suggest that the choice of the progestagen component in combined HRT is of importance regarding breast cancer risk; it could be preferable to use progesterone.”  (Progestagen – also spelled progestogen - is the class of hormones that includes progesterone and progestins.)      
Breast Cancer Res Treat. 2008; 107(1):103-111.
  The Developmental Endocrinology Branch, National Institutes of Health, had previously shown that the addition of testosterone (not METHYLtestosterone) to conventional hormone therapy for postmenopausal women does not increase and may indeed reduce the risk of breast cancer.     
Menopause. 2004 Sep-Oct;11(5):531-5. 
  A study of the influence of topically administered estradiol and progesterone on human breast tissue concluded that progesterone administration decreases estrogen-induced breast cell proliferation by 400%.
Fertil Steril. 1995;63(4): 785-791.

We work together with physicians and nurse practitioners and their patients to customize Bio-Identical Hormone Replacement Therapy in the most appropriate dose and dosage form for each woman. We will be happy to answer any questions.

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