Medical therapy to induce a castration is generally intended for use in patients who have advanced disease not curable by surgery, radiation therapy, or cryotherapy. Over the last decade however, there has been more widespread use of these treatments in patients who do not have advanced disease but are not candidates for curative therapy for many reasons including advanced age or other coexisting diseases that do no allow for them to undergo curative techniques.
There are presently two major categories of drugs that provide medical castration for the treatment of advance prostate cancer, LHRH agonist and LHRH antagonists.
The LHRH agonists are presently the drugs that are most commonly used to provide androgen ablation (suppression of male hormones). These drugs are administered in a series of ways including injections that are administered monthly, every 3 months, every 4 months or every 6 months. Additionally there is a form of the drug that is administered in the form of a small capsule that is inserted under the skin yearly.
This group of drugs is a chemical that simulate a substance that normally occurs in the body and released by the pituitary gland. Initially the effect of this drug is a initial increase in the testosterone levels know as the “flare response”, however over time, testosterone production is shut down. This flare response is a drawback to the use of these drugs as it can result in a worsening of ones urinary symptoms or more importantly an increase in bone pain. In patients who have metastatic bone disease, this can cause the metastasis to temporarily worsen or cause more symptoms.
LHRH antagonists are newer category of agents that also helps to lower the testosterone levels. This type of drug blocks the normal receptors in the pituitary gland. By doing this, the testosterone levels immediately fall because no further testosterone is being produced. These drugs result in a rapid and sustained suppression of testosterone. The drug is administered by injection every 28 days.
The initial clinical studies that were done for this agent Firmagon (degarelix) demonstrated a greater castration rate as well as a more rapid fall in PSA when compared to luprolide (LHRH agonist), as well as the long-term suppression of testosterone.
These studies provide good evidence that this category of drugs prevents surges of testosterone during treatment, as well as limiting the likelihood of testosterone escapes during therapy.