Breast Cancer Risk and Hormone Replacement Therapy

The association of breast cancer risk with unopposed estrogen therapy (ERT) or combined estrogen and progestin therapy (hor-mone replacement therapy [HRT]) remains controversial despite the publication of more than 50 epidemiologic studies during the last 25 years. The current prevailing opinion appears to be that “es-trogen replacement therapy [ERT] modestly increases the risk of breast cancer, and HRT increases the risk more than ERT.”1 However, it should be pointed out that two of the recent studies2,3 that support this opinion both mention that medroxyprogesterone acetate (MPA), a synthetic progestin, was used in the majority of the women studied. In Part 2 of this series,4 it was clearly demon-strated that synthetic progestins and progesterone are complete-ly different hormones. In the final segment of this article, additional evidence of the vast differences between synthetic progestins and bioidentical progesterone is again presented