Progesterone is a hormone that is normally found in women and it reaches particularly high levels during pregnancy. Progestins are synthetic drugs that mimic the biological actions of progesterone and they have been widely prescribed to women. This learning project allows Wikiversity participants to explore health-related topics that involve progesterone and synthetic drugs that act on progesterone receptors.
Progesterone, progestins and breast cancer
The Wikipedia articles on breast cancer and progestins do not mention that breast cancer rates appear to be increased by progestin use. Wikipedia articles for the Women's Health Initiative and Hormone replacement therapy do mention some of the clinical trial results that link progestin use to increased breast cancer risk. Recent studies suggest mechanisms by which progesterone receptors might stimulate breast tumor growth. The Wikipedia article on Bioidentical hormone replacement therapy raises the question: might progesterone use pose less breast cancer risk than use of synthetic progestins?
Why are progestins so widely prescribed?
Progestins are widely used by both younger women and older women. Younger women of reproductive age often use progestins for hormonal contraception. Older women have frequently been prescribed combinations of estogen and progestins as Hormone replacement therapy when endogenous levels of estrogen decline. Combined estrogen and progestin administration is used to limit the incidence of estrogen supplement-induced endometrial cancer.
This is a running list of news reports related to progestrone, progestins and related health issues such as breast cancer.
October 30, 2007. "Wyeth is facing more than 5,000 lawsuits from those who believe they were harmed by the hormone replacement drugs, which have been used by millions of women to control the effects of menopause." Wyeth is the manufacturer of Premarin and Prempro, a mixture of medroxyprogesterone and Premarin.
The Women's Health Initiative estrogen-plus-progestin study reported an increased rate of breast cancer for women using Prempro. The Food and Drug Administration now requires that the Women's Health Initiative results for breast cancer be provided to patients who use Prempro (Label).
Brest cancer incidence
December 15, 2006. Following the release of results from the WHI Prempro clinical trial (see above), "Within six months, the drug's sales had fallen by 50 percent." Breast cancer incidence also declined during this time: "The reason, researchers believe, may be that millions of women during that time abandoned hormone treatment for the symptoms of menopause"
Epidemiological studies report that since women started to become aware of the risks associated with progestin use, decreases in incidence of breast cancer parallels the decline in progestin use, consistent with the known increased risk of breast cancer among women who use progestins.
Using progesterone rather than progestins
January 16, 2007. The North American Menopause Society (NAMS) is a nonprofit organization concerned with menopause. T.V. correspondent Dr. Emily Senay reported that the NAMS has urged doctors not to prescribe natural hormones like progesterone for menopausal women Large clinical trials have not been performed to test the efficacy and safety of natural hormones like progesterone for treating the symptoms of menopause.
Who would pay for clinical research studies on progesterone? One possibility is that government funding would be provided in an attempt to find alternatives to synthetic progestins, but is there a level playing field for discussion of such studies when drug companies make large profits from synthetic progestins? The International Academy of Compounding Pharmacists has suggested that The North American Menopause Society is not an independent voice because it is supported by progestin manufacturers.North American Menopause Society’s Ties to Wyeth Pharmaceuticals
One recent reviewer concluded that there needs to be more research on bioidentical hormones and that there is, "evidence to support their preferred use over that of their synthetic cousins." Other reviewers have reached the opposite conclision. 
A major concern for use of progesterone rather than synthetic progestins is that progesterone is rapidly metabolized in the body. There are many different formulations of mixtures of estrogen and progesterone and various methods for administering them. There has been concern about quality control for progesterone both in terms of variability in amounts and efficiency of absorption. Some women have used bioidentical hormone treatments for extended periods of time without monitoring for possible stimulation of uterine tissue growth.  Women should not assume that bioidentical hormone treatments are safe just because they use natural hormones. Supplements containing natural estrogen can cause endometrial cancer.
- Progesterone Receptors Upregulate Wnt-1 To Induce Epidermal Growth Factor Receptor Transactivation and c-Src-Dependent Sustained Activation of Erk1/2 Mitogen-Activated Protein Kinase in Breast Cancer Cells by Emily J. Faivre and Carol A. Lange in Mol Cell Biol. (2007) Volume 27 pages 466–480.
- Progestins and progesterone in hormone replacement therapy and the risk of breast cancer by Carlo Campagnoli, Françoise Clavel-Chapelon, Rudolf Kaaks, Clementina Peris, and Franco Berrino in J Steroid Biochem Mol Biol. (2005) Volume 96, pages 95–108.
- Judge dismisses hormone case against Wyeth, Reuters, 30 October, 2007.
- "Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial" by J. E. Rossouw, G. L. Anderson and R.L. Prentice in Journal of the American Medical Association (2002) Volume 288, pages 321-333.
- Breast cancer rates drop 15% from August 2002 to December 2003 by Gina Kolata December 15, 2006, in International Herald Tribune.
- "Decline in breast cancer incidence due to removal of promoter: combination estrogen plus progestin" by G. A. Colditz in Breast Cancer Res. (2007) Volume 9, page 108.
- Testing Of Bioidentical Hormones Urged. The Early Show medical correspondent Dr. Emily Senay and co-anchor Julie Chen. January 16, 2007
- A comprehensive review of the safety and efficacy of bioidentical hormones for the management of menopause and related health risks by Deborah Moskowitz in Altern Med Rev. (2006) Volume 11, pages 208-223.
- "Bioidentical hormone therapy: a review of the evidence." by M. Cirigliano in J. Womens Health (Larchmt) (2007) Volume 16, pages 600-631.
- Three cases of endometrial cancer associated with "bioidentical" hormone replacement therapy by John A Eden, Neville F Hacker and Michael Fortune in Med J Aust. (2007) Volume 187, pages 244-245.