Hormone therapies work in three main ways:

The first way is to block the production of the bodies own hormones. One straightforward way is to surgically remove the ovaries or testes. Some drug therapies chemically do the same thing by blocking the signal from the brain to the ovaries or testes - these include goserelin (Zoladex), leuproelin (Prostap) collectively called LHRH blockers. Other drugs in this category work by stopping the production of oestrogen from the adrenal glands. These only work in post menopausal women and the three most commonly used in the UK are anastrazole (Arimidex), exemestane (Aromasin) and letrozole (Femara).

The second way hormone therapies work is to fool the signal pathway between the brain (pituitary) and the ovaries or testes by increasing the blood levels of another hormone produced in the ovaries so in turn the brain thinks they are producing too many hormones including oestrogen and as a consequence switches off the driving signal by itself - this results in reducing the blood level of oestrogen. Drugs which act in this way include Medroxyprogesterone acetate (Provera), Megestrol acetate (Megace), stilboestrol and cyproterone acetate.

The third way to stop the bodies hormones stimulating cancer cells to grow is to block the cells ability to read the signal from the hormones in the blood stream. Cancer cells have receptors which when blocked they cannot be influenced by the bodies hormones, despite often normal levels in the blood stream. The most well known is called oestrogen receptor and can be blocked with tamoxifen and toremifene (selective oestrogen receptor modifiers -SERM's). These receptors can be measured by performing a special test on the tissue removed from the tumour (oestrogen receptor positive). In prostate cancer the receptors are called androgen receptors, Although they are not easy measured they can be blocked with drugs such as bicalutamide (casodex), Flutamide (Drogenil) and Buserelin (suprefact).