Some quick history here, first they gave postmenopausal women estradiol but this was soon to be found to increase cancer rates, then they started giving them synthetic progesterone/estrogen analogs (like AAS are analogs of test) that were active as both progesterone and estrogen. Decades later (I think in the 90s or just after) this was also found to increase cancer rates. Along came 'bio-identical' replacement soon after, this is based on giving estrogen, progesterone, and testosterone. It turns out testosterone was the missing component that helped protect the cancer-causing effect.
It should be noted that the synthetic progesterone/estrogen drugs alone, not using testosterone, is still the standard of care and bioidentical treatment is still an 'alternative medical treatment' to the AMA, there is also a lack of long term studies on bio-identical treatment and they may turn out not to protect against cancel, but it sure seems like the way to go from what I know, and besides the alternatives are worse.
The key is definitely constant bloodwork and getting the dosage perfect, this can change over time, especially with topicals, as the skin will sometimes become resistant to absorption with repeated applications and different areas can have different absorptions...