Yes, synthetic progestins increase breast cancer, but there is no evidence that progesterone does the same. Quite the contrary. Below is my argument in favor of natural progesterone as a preventive for breast cancer, with reference to the Fournier studies that address this issue.
“Experts” who are saying that synthetic progestins increase breast cancer risk are right, but, we’ve known that since 2002. Unfortunately, these same “experts” are now claiming an association of natural progesterone with breast cancer by default. They espouse that there is no clinical evidence to show natural progesterone is any safer than synthetic progestins. Unfortunately, this is an incorrect assumption and they have not done their homework.
A recent study published in the prestigious New England Journal of Medicine (NEJM) casts a shadow on the common use of testosterone therapy in older men for boosting their energy and vitality. An FDA-approved testosterone gel was shown to significantly increase risk for adverse cardiovascular, respiratory, and dermatological events in men 65 or older who had impaired mobility and increased health risks.
These unexpected negative results fly in the face of decades of good research on testosterone therapy in older men showing it to be beneficial to the cardiovascular system, and improve sexual function, mood, energy level, and muscle and bone mass and strength.
Dr. David Zava explains how and why bioidentical progesterone can cause breast tenderness in some women.
Over the past few years controversy has erupted over the risk of developing breast cancer with estriol therapy. A study from Sweden (Rosenberg et al, 2006) suggests that estriol can increase risk of lobular carcinoma when used for five years or less, and decrease the risk when used for more than five years. Unlike estriol however, oral estradiol and progestins continue to increase risk after five years. The results of this study may appear to be confusing, but can be explained by the differences in cancer initiation and cancer promotion by different types of estrogen.