Progesterone triggers breast cancer promoting genes

Kathleen Blanchard's picture

Researchers at Michigan State University have gained new insight into how the hormone progesterone promotes breast cancer. Scientists have discovered that progesterone activates genes that cause inflammation in the mammary gland, (breast gland) that in turn promote breast cancer.

Progesterone is necessary for normal female growth and development, and is known to increase breast cancer risk and inflammation. During puberty, the inflammatory response is how breast development occurs. One type of macrophage, (white blood cell) moves into the breast during inflammation, as part of the body’s normal defense that also opens the door to breast cancer development.


Physiology professor Sandra Haslam, co-author of the paper and director of the Breast Cancer and the Environment Research Center at MSU explains, “Macrophages also may promote the development of tumors, such as breast cancer, as they make blood vessels to deliver nutrients and can clear the way for tumors to growth. Long-term exposure to progesterone, such as that which occurs in menopausal hormone therapy, may encourage growth of tumors.”

Progesterone also turns on a gene switch. Progesterone regulates 162 genes in cells during puberty, 104 genes in the cells of adults, and 68 genes during development and adulthood. A portion of those genes also produce inflammation from the manufacture of small proteins, called chemokines. Dr. Haslam says “All of these processes may be relevant to the development of breast cancer”, from exposure to progesterone.

Breast cancer rates have declined with less use of progesterone hormone therapy following menopause. The research could lead to better breast cancer treatments, because now scientists undestanding how genes act in response to progesterone that to promote tumor growth in breast tissue.

MSU News


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