The normal ovary produces abundant testosterone (T) in addition to estradiol (E₂) and progesterone, but usually only the latter two hormones are “replaced.” Balanced Hormone replacement includes androgens (T) which normally inhibit estrogen-induced mammary epithelial proliferation (MEP) and thereby may protect against breast cancer.

In a study on monkeys, a small physiological dose of T added to standard estrogen therapy almost completely attenuates estrogen-induced increases in MEP, suggesting that the increased breast cancer risk associated with estrogen treatment could be reduced by T supplementation. Testosterone reduces mammary epithelial estrogen receptor (ER) α and increases ERβ expression. Think ERβ as better and α as awful.
In addition to the estradiol (E₂) we recommend considering estriol (E3) as well.