In normal people, 90% of the androgens in the blood come from the testes and another 10% from the adrenal glands.
Orchiectomy eliminates the vast majority of androgens, allowing serum testosterone levels to be reduced to less than 5% to 10% of their original levels, while dihydrotestosterone (DHT), the active androgen inside the prostate that sustains cancer cell growth, is reduced by only about half. The DHT in the prostate still remains at about 40%, and this DHT is mainly of adrenal origin.
So, it is recommended that patients take oral anti-androgen drugs (such as bicalutamide and flutamide) to block the effects of androgens secreted by the adrenal glands, so that the supply of androgens to cancer cells can be completely blocked and the prostate cancer can be “starved” to death.