ISSUE
46
June 2011
HORMONE THERAPY FOR PROSTATE CANCER
by Stephen Connolly
Prostate cancer ranks among the most common cancers, but unlike many other forms of cancer, prostate cancer cells are uniquely dependent on androgens (the hormone testosterone and its related biochemicals) for sustenance and growth. If prostate cancer cells are deprived of androgens, they die. This opens an area of effective treatment for prostate cancer called hormone therapy. The majority of androgens (95 per cent) are produced by the testicles under the control of the hypothalamic-pituitarygonadal (HPG) axis. The remainder are produced by the adrenal glands. The hypothalamus, located centrally within the brain, produces Luteinising-Hormone Releasing Hormone (LHRH) which in turn stimulates the pituitary gland, located at the base of the brain, to produce Luteinising Hormone (LH), which in turn stimulates the gonads (testicles) to produce the vast majority of the testosterone normally found in the body. In 1941, Charles Huggins wrote perhaps the most influential single publication in prostate cancer, leading to the award of a Nobel Prize for medicine in 1966. He described the favourable effect of orchidectomy (the removal of the testicles) on men with metastatic prostate cancer. Orchidectomy reduces the levels of testosterone. Testosterone levels can also be reduced by the administration of medications to ‘turn-off’ testosterone
production via the HPG axis, or less commonly, by interruption of the normal biochemical pathways of testosterone synthesis. Hormone therapy has now evolved to become the mainstay of management for men with advanced prostate cancer. Surgery (to remove the prostate in its entirety) or radiation therapy are better options for men with early prostate cancer in whom a complete ‘cure’ can be achieved. Medical practitioners managing prostate diseases frequently talk in broad terms about ‘hormone therapy’ or ‘androgendeprivation therapy’, which also includes medications to block the downstream effects of androgens, without having any effect on testosterone levels. Examples include androgen receptor antagonists (anti-androgens, described in more detail below). Not all hormone therapy is directed at cancer, and some are more suited to benign prostate diseases such as BPH. CONTINUED PAGE 3