Breast Cancer Research for Your Doubting Doctor

This is the article to take to your doubting doctor.

It’s pretty hard to get goose bumps reading a scientific review article, but as I was reading “Pregnancy, progesterone and progestins in relation to breast cancer risk,” by a group of Italians led by Carlo Campagnoli, my hair stood on end. Here, in one eloquently worded, organized and argued paper was the same basic argument that Dr. Lee, Dr. Zava and myself made our 2002 book, What Your Doctor May Not Tell You about Breast Cancer about why progesterone is protective against breast cancer and progestins cause it. However, since the article was written four years after our book, it cited even more good research to prove the point.

If you’re facing a doctor who doesn’t understand the relationship between progesterone, estrogen, progestins and breast cancer, suggest that he or she read this paper.

What You Need to Know about Progesterone and Breast Cancer

Here are some of the major points made by the authors:

  • It’s the synthetic progestins that contribute to causing breast cancer—not progesterone.
  • Even one full-term pregnancy is remarkably protective against breast cancer, probably because progesterone and other pregnancy hormones cause permanent changes in breast tissue that are protective, and because progesterone levels are very high in the last few weeks of a full-term pregnancy.
  • Women with the highest progesterone levels, and the highest progesterone/estradiol levels during pregnancy, have the lowest risk of breast cancer.
  • It’s estrogen, not progesterone, that stimulates proliferation of breast cells.
  • They cite five studies showing that menstruating women with the lowest mid-cycle progesterone levels have the highest risk of breast cancer.
  • They cite the E3N French HRT studies and note: “It is important to realize that recent findings relating to the use of natural progesterone, in sharp contrast to those referring to the use of progestins, are reassuring. …It is probable that the increase in BC risk found in other studies with HRT is related to the fact that synthetic progestins, rather than progesterone, were used.”
  • Insulin resistance, hyperinsulinemia and high blood glucose (caused by being overweight, eating too much sugar and refined carbs, not exercising, stress and not enough sleep) are associated with an increased risk of breast cancer.


Campagnoli C, Abba C, Ambroggio S, Peris C, Pregnancy, progesterone and progestins in relation to breast cancer risk. J Steroid Biochem Mol Biol, 2005 Dec;97(5):441-50.

The article Bioidentical Hormones and Breast Cancer Risk will give you more evidence-based research showing that bioidentical hormones do not increase breast cancer risk and used wisely, may even reduce it.

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