Men with more advanced prostate cancer often undergo treatment to reduce levels of testosterone, which drives tumor growth. Now, a new study shows that this so-called androgen deprivation can be rapidly reversed.

In the study, testosterone levels that were effectively supressed with a hydrogel implant releasing the hormone-suppressing drug histrelin rebounded rapidly after removal of the implant. However, the rebound was not as swift when a similar therapy called depot GnRH was injected, Israeli researchers report.

To examine the reversibility of androgen deprivation, Dr. Alon Fridmans of Shaare Zedek Medical Center, Jerusalem, and colleagues studied 22 men with prostate cancer.

Of these, seven had been treated via a hydrogel implant containing histrelin for up to 3 years, eight had been treated with long-term depot GnRH super agonists and the remaining seven, who had had no prior hormonal therapy, received the testosterone-suppressing drug bicalutamide.

In the implant group, levels of both testosterone and luteinizing hormone (LH), which drives up testosterone levels, were reduced to the castration range. When the implant was removed, LH increased within 6 weeks and testosterone also increased.

However, patients in the depot group showed suppression of testosterone, LH and prostate specific antigen for at least 9 months after their last injection.

In six of the seven hormonal therapy-naive patients, there was a significant increase in testosterone and LH within 7 days of starting bicalutamide.

The researchers thus point out that histrelin implants allow simple implementation of intermittent hormonal therapy.

However, because of the long-term effects of depot injection, they conclude that serum testosterone must return to normal levels before depot injection interruption can be construed as “bona fide intermittent therapy.”

Moreover, Fridmans told AMN Health because of these lasting effects, it also “may be possible to space GnRH analog administration at longer time intervals rather than the 2-3 monthly intervals currently recommended.” The study findings appear in the March issue of the Journal of Urology.

SOURCE: Journal of Urology March, 2005.