It has long been known that prostate cancer is to some extent dependent on and nourished by the male sex hormone, testosterone. This is one of a group of hormones known as androgens. Since testosterone stimulates the growth of prostate cancer cells, depleting or ablating the body's testosterone tends to shrink the size of many tumors, specifically, those that are hormone-sensitive. The goal of hormonal therapy is to decrease the production of testosterone in the body, inhibiting the growth and progression of the cancer. Hormonal therapy, also known as Androgen Ablation Therapy (ADT), can shrink a man's prostate by 50%.

Hormonal treatment is typically optional for patients having intermediate risk features but encouraged for patients having high risk features. With the low-risk or mildly aggressive cancers, unless the size of the gland is markedly large, we don't normally give the conventional hormonal therapy (combined hormonal blockage using an anti-androgen and an LHRH agonist), since this form of therapy may result in typically temporary although potentially longer lasting unwanted side effect such as erectile dysfunction, hot flashes and potential fatigue.

We often prescribe a milder, modified version of hormones which do not reduce testosterone but rather act as blocking agents (e.g. oral anti-androgens), not allowing the testosterone to bind with the prostate cancer receptors. These are commonly combined with other oral agents (e.g. 5 alpha-reductase inhibitors) which do not allow testosterone to convert to dihydrotestosterone (DHT), a metabolite which is 10 times as potent as testosterone in stimulating prostate cancer growth. This type of hormonal therapy is just enough to arrest the cancer and allow the patient to make a more relaxed decision about treatment, without the side effects associated with formal ADT.