>>76346618No, i'm talking about main pathway of breast growth, mediated by even miniscule levels of estradiol and suppressed by testosterone in natal males.
Testosterone strongly decreases expression of ER-alpha, a receptor responsible for breast growth and mammary development. On top of that, androgen receptors are also present in mammary tissue and tied to its development, with testosterone activation acting as a downregulator of development.
At the same time, even small amounts of estradiol will bind to ER-alpha and signal for breast growth. It might be slower with low estradiol of males, but it will get there. Again - CAIS women with what are near-male estradiol levels and no progesterone end up with above-average growth, given time.
This has nothing to do with prolactin, testosterone is simply an important moderator of breast development in every body.