Prostate drug holiday will change the standard of care for men with recurring prostate cancer

06 June 2011

Toronto -

Unequivocal results from a clinical trial released today at the annual meeting of the American Society of Clinical Oncology reveal that men with prostate cancer who are treated with intermittent courses of androgen-suppressing therapy will live as long as those receiving continuous therapy.

The Canadian Cancer Society-funded clinical trial, led by the NCIC Clinical Trials Group (CTG), has shown conclusively that if men choose intermittent over continuous androgen-suppressing therapy their life is not shortened.

“We have known since the mid-1990’s that androgen suppressive therapy could be used in an interrupted fashion, but we didn’t know until now that men were not sacrificing length of life in the hopes of having a better quality of life,” says Dr Juanita Crook, principal investigator and radiation oncologist with the BC Cancer Agency. “The results of this trial will change the standard of care.” Dr Crook co-led the study with Dr Laurence Klotz.

The standard treatment until now has been to use continuous therapy but this is expected to change as a result of these findings. These findings also have significant economic and quality of life implications. Patients on the intermittent therapy used only one-third the amount of the drug, which is both very costly and has numerous troublesome side effects, including impotence.

“This year alone, more than 25,000 Canadian men will be diagnosed with prostate cancer, which is a heavy burden for these men and for the people who love them,” says Dr Christine Williams, Director of Research, Canadian Cancer Society. “These tremendously important research findings may significantly reduce the side effects of cancer treatment and improve the overall quality of life for those men who suffer a recurrence after their initial treatment.”

Since the growth of prostate cancer depends on the male hormone testosterone, one of the commonly used treatments is a form of “hormone therapy” to lower testosterone (androgen) levels. Men who took part in this clinical trial had initially undergone surgical or radiation treatment for their prostate cancer but subsequently experienced elevated PSA levels (prostate-specific antigen) indicating that their cancer had returned. Nearly 1,400 men participated in the trial which recruited patients from 1999 until 2005. Most were from Canada, others were from the US and the UK.

Patients in the trial were randomized into two different groups: the control group of men received slow-release injections of a drug called an LHRH blocker (luteinizing-hormone-releasing hormone) continuously usually at 3-month intervals. The experimental group received the same drug but in treatment cycles that were 8 months long, interrupted for extended “drug holidays” lasting several months to years. These men were monitored every two months using the PSA test. If a patient’s PSA levels rose while off treatment, he would then resume treatment with the LHRH blocker for another 8-month cycle until his PSA levels dropped again, and so on.

The follow-up period of the trial was stopped early because a planned mid-trial analysis, reviewed by an independent data and safety monitoring committee, unequivocally demonstrated no difference in survival outcome between the two groups of men.

Patients receiving intermittent courses of the testosterone-suppressing drug also reported better quality of life, presumably because of fewer or less intense side effects. A more detailed assessment of this aspect of the trial along with a formal economic analysis are planned. Androgen-suppressing therapy side effects include hot flashes, sexual impotence, growth of breast tissue, insomnia, weight gain, worsening of diabetes, loss of muscle mass and osteoporosis. These side effects are due to the chemical castration produced by the drugs.

About the NCIC Clinical Trials Group
The NCIC Clinical Trials Group (NCIC CTG) is a national research program of the Canadian Cancer Society and receives programmatic funding, including for this trial, from the Canadian Cancer Society Research Institute. Additional support for the trial was provided by Sanofi-Aventis.

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