I wonder if this has an effect on the proliferation of endometriosis lesions as well?
(BC=breast cancer) "In vitro studies have shown that progestins derived from 19-Nortestosterone exert an estrogen-like proliferative effect on BC cell lines [125,126]. The effect is probably mediated by reduced 5α metabolites, which interact with α and β estrogen receptors [127]. One might also conceive, however, that progestins with androgenic activity stimulate BC cell proliferation via in...teraction with androgen receptors....More importantly, many of the progestins used have several non-progesterone like actions that potentiate the proliferative effect of estrogens on breast tissue and estrogensensitive cancer cells. We therefore suggest that when HRT is indicated, preparations containing progesterone and not a synthetic progestin should be used, according to a sequential or cyclic-combined regimen. In this way the risk of endometrial cancer is minimized without increasing the risk of BC." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1974841/
"...We find, as shown previously (42–44), that estradiol is not required for establishment of endometriosis-like lesions.... Finally, endometriosis-like lesion growth is mediated predominately by estradiol signaling via ERα to increase lesion size, fluid volume, increased epithelial cell height, and epithelial cell proliferation...." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3404357/