Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study.

Authors: Fournier A, Berrino F, Clavel-Chapelon F.

Publication Year: 2008

Citation: Breast Cancer Res Treat 2008;107(1):103-11.

This large multicenter study in France followed 80,377 postmenopausal women for up to 12 years, and looked in particular at whether the type of progestogen used in combination with estrogen made a difference to the risk of developing breast cancer in those women who used hormone replacement therapy (HRT).  The estrogen in HRT is primarily transdermal estradiol in France.  Compared with those women who did not use HRT at all, women using estrogen alone had a 1.29-fold increased risk of developing breast cancer; women using estrogen plus natural progesterone had the same risk as women using no HRT.  In women using synthetic progestins in combination with estrogen, the particular progestin used made a difference to breast cancer risk; women using dydrogesterone had a 1.16-fold increased risk of breast cancer, but those using other progestins had a 1.69-fold increased risk of breast cancer, compared to women not using HRT.  The authors note that dydrogesterone is the progestin most similar to natural progesterone in its chemical structure and pharmacological effects.