Estrogen & Progesterone’s Role in Breast Cancer

There’s often a lot of talk about estrogen when it comes to breast cancer. But what isn’t well known is that while estrogen can fuel a tumor’s growth, progesterone puts the brakes on that growth.

A 2016 study led by Cambridge-based Cancer Researcher Dr. Jason Carroll found that progesterone, via the progesterone receptor, is affecting how the estrogen receptor works. He found that at least 470 genes were controlled differently when both progesterone and estrogen were present (compared to just estrogen alone). The progesterone receptor was actually ‘reprogramming’ the estrogen receptor, changing the genes that it influences. When it came to cancer cells, progesterone seemed to cause the cells to stop growing as quickly. This explained why the receptor itself is the best reason why women who have both estrogen and progesterone receptors have a better outlook than those with just estrogen receptors.

Understanding the difference between natural progesterone (made by the human body) and synthetic progesterone is very important. While natural progesterone has an anticancer effect, synthetic progesterone (found in birth control pills and hormone replacement supplements) does not.

P53 is a repair gene, which protects cells from being cancerous. If synthetic progesterone (which does not stimulate the production of P53) is present on the receptors, natural progesterone will not be able to occupy the receptors.

Dr. Carroll’s research is a big step forward in understanding the role of progesterone receptor in breast cancer. Before this study, its presence was simply considered an indication of how good a woman’s chances of surviving were.

The study can be found in the journal Nature or you can read a summary by Elyn Jacobs, breast cancer survivor and holistic cancer strategist.