I've read 5 recent papers that discuss the use of estrogen as an alternative treatment to ADT (Lupron, etc.). The new data looks very favorable.
A bit of history. Huggins discovered this effect around 1941-44, and he found that high doses of estrogen (estradiol) efficiently castrated men, which, in turn, reduced prostate cancer. Soon after that, they prescribed DES, which, indeed, castrated men. But, it had bad side effects, primarily blood clots and other CV effects. So, it fell into disfavor.
Recently, in the last 10 years, researchers have used three, different estrogen sources: (1) estradiol phosphate (IM), (2) transdermal estrogen (estradiol E2) patch, and (3) a contraceptive pill with estetrol (E4), a different form of estrogen. Since none of these new sources are oral, they don't pass through the liver, which prevents the bad CV effects from happening.
The new estrogen sources have no difference in PCa mortality rates, according to one paper. Importantly, side effects are much less than ADT, including, but not limited to, reduced CV side effects, reduced hot flashes, reduced bone loss, reduced fatigue, improved libido, and improved Quality of Life (QoL). In most cases, bone mineral density stayed the same or increased over time with estrogen treatment.
The only downside of estrogen treatment is increased gynecomastia (breast enlargement) and increased nipple sensitivity.
If you send me your email address, I will send you .pdfs of the papers (one from 2023).
Bob