Endogenous estrogen, androgen, and progesterone concentrations and breast cancer risk among postmenopausal women.

Authors: Missmer SA, Eliassen AH, Barbieri RL, Hankinson SE.

Publication Year: 2004

Citation: J Natl Cancer Inst 2004; 96(24):1856-65.

Blood progesterone levels were found not to be related to breast cancer risk in this first study to investigate this in postmenopausal women. The occurrence of progesterone receptor positive tumors was the tumor type most strongly affected by all the circulating steroid hormones measured except for progesterone.  Higher levels of endogenous estrogens and androgens were significantly correlated with increasing breast cancer incidence.  This suggests that circulating natural progesterone does not increase breast cancer risk.

http://www.ncbi.nlm.nih.gov/pubmed/15601642