'Estriol: Safety and Efficacy' Review http://www.altmedrev.com/publications/3/2/101.pdf
Estradiol and Esterone can convert into each other. Very little of either converts into Estriol by the liver.
"Most estradiol, however, is bound to sex-hormone binding globulin (SHBG), so only a portion of the circulating estradiol is available for entry into cells. On the other hand, estriol has a much lower affinity for binding to SHBG; therefore, a greater percent is available for biological activity."
Androstenedione converts into estriol.
"While estriol appears to be safer than estrone and estradiol and, in some situations, provides some protection against carcinogenesis, it appears its use in breast cancer patients with active disease or with patients at high risk for breast cancer should be approached with caution."
Estradiol and Esterone can convert into each other. Very little of either converts into Estriol by the liver.
"Most estradiol, however, is bound to sex-hormone binding globulin (SHBG), so only a portion of the circulating estradiol is available for entry into cells. On the other hand, estriol has a much lower affinity for binding to SHBG; therefore, a greater percent is available for biological activity."
Androstenedione converts into estriol.
"While estriol appears to be safer than estrone and estradiol and, in some situations, provides some protection against carcinogenesis, it appears its use in breast cancer patients with active disease or with patients at high risk for breast cancer should be approached with caution."