This study looked at 100,000 women and compared the risk of breast cancer between those using estrogen (mostly estradiol) and progestogens in the form of progestins (synthetic progesterone) and of estrogen with natural progesterone. The results showed a lower risk of breast cancers in those that used natural progesterone as compared to those using synthetic progestins. A landmark study that should be read by the lay-person as well as the medical professional. To fully understand this study, you need to understand the definitions of the terms “progestogens”, “progestins” and “progesterone”. Those definitions can be found on the Research Tab under Introduction. E3N Study