Progestins stimulate breast cancer cell proliferation mainly through binding to progesterone receptors.40 Progestins also bind to androgen receptors, whose signaling has antiproliferative and proapoptotic effects,41 and has even been explored as a therapeutic target in breast cancer.42,43 While desogestrel has slightly higher progesterone receptor affinity, it also shows considerably lower binding to androgen receptors38 compared to levonorgestrel,44 which agrees with findings in this study. This evidence concerns the gene PGR and breast cancer.