By ICIM Member Alexander Mostovoy HD, DHMS, BCCT: Progesterone and Cancer Prevention

Progesterone reduces estrogen’s stimulating of breast cancer growth with several well known biochemical events that lead to tumour growth:
Progesterone increases the level of enzymes that convert cancer prolific estrogen (estradiol) to inactive cancer protective estrogen (estrone sulfate).
Progesterone inhibits estrogen activity in the breast tissue and decreases the probability of clotting.
Progesterone prevents angiogenesis known to be a major contributor in early stage of breast cancer tumour formation and growth.
Progesterone prevents vasodilatation caused by excess estrogen and thus acts as an anti metastatic agent
Progesterone activates natural killer cells that function as in immune defence mechanism destroying cancer cells.
Progesterone has a calming effect, helps with perceived  stress, thus lowering cortisol production by the adrenals
Here’s the critical point about progesterone for breast cancer prevention: synthetic progestins promote breast cancer and heart disease, while natural progesterone beneficially lowers breast cancer and heart disease risk. Progestin (synthetic) is NOT Progesterone (natural). Unfortunately many physicians believe progestins to be equivalent to progesterone. This is a mistake.
The enzymes needed to metabolize progesterone are present in the human body, not so with progestin. Further, the biochemical structures of several synthetic progestins have carbon-carbon bonds, which are not present in the hormones that humans have. Thus synthetic progestin has well known detrimental effects on women’s health while progesterone has beneficial effects on breast health and cancer prevention.
Of course, your breast cancer prevention strategy has to include other contributing factors, such as healthy diet, physical activity, avoidance of pollutants, stress reduction and possibly natural progesterone therapy. Investigate and see if this will work for you.