For patients facing advanced prostate cancer, taming the testosterone is crucial. 

“Testosterone is like the fuel for prostate cancer to grow,” says Dr. Joseph Chin, Professor of Urology and Oncology at the University of Western Ontario. Any type of therapy that does this is called androgen deprivation therapy (ADT), and the one common class of drug is known as a GnRH agonist. 

There’s a chain, explains Chin, that starts in the brain. The hypothalamus sends the gonadotropin-releasing hormone (GnRH) to control the pituitary gland, which in turn secretes the luteinizing hormone (LH), which sends a message to the testicles, telling them to make testosterone. 

Changing the signals

The GnRH agonist is a synthetic  GnRH.  “It’s kind of like an imposter,” says Chin. “It gets in there, and gives a different signal, deliberately shutting off the pituitary, which then won’t send any more signals to the testicles and then the testicles don’t make any more testosterone."

“New dosing options can allow patients to go as long as six months between shots.”

Without the fuel, the cancer may regress. “It’s very effective therapy, just not curative,” says Dr. Laurence Klotz, Professor of Surgery at the Sunnybrook Health Sciences Centre, University of Toronto. 

Less pain, longer life

By slowing the production of testosterone, this class of drugs can prolong survival, says Klotz. “Men with metastatic prostate cancer may have vertebral metastasis which is giving them back pain or metastasis in the pelvic bones and they get hip pain. This class of drugs dramatically reduces that.”

However, he says these drugs are now commonly given to prolong survival in men with a rising prostate-specific antigen (PSA) level after radiation and surgery, and also used with radiation treatment. “There the goal is to cure the patient. There’s a synergistic effect between the radiation and the hormone therapy,” says Klotz. 

The drug is administered by injection, and new dosing options can allow patients to go as long as six months between shots. 

Reversibility

Side effects can include less energy and hot flashes, says Dr. Chin, and over time the drugs may become less effective, but it’s more palatable than other options.  “Taking away the testicles with surgery obviously isn’t all that attractive, though it’s very effective and quite economical,” says Chin. 

The beauty of these drugs is they are reversible, says Klotz. “You can stop them, the testosterone recovers, the patient gets his libido back and it may be that he’s off treatment for two, three, or four years before he has to go back on.”