Impotence after prostate cancer treatment can be as high as 97 per cent for some treatments a national research conference heard on Thursday.

Researchers presented the results of a five year study to the Clinical Oncological Society of Australia's Annual Scientific Meeting, claiming the findings shed new light on the extent and duration of one of the most common side-effects of prostate cancer treatment.

Lead researcher and Cancer Council Epidemiologist, Dr David Smith, said the population wide study compared sexual function and sexual 'bother' in more than 1600 patients and 500 controls.

"Impotence is a common side-effect of prostate cancer treatment, along with incontinence," Dr Smith said. "There is a widespread perception that symptoms ease with time, but there has been little in the way of research to confirm whether this is the case.

"Our study shows that for conventional prostate cancer treatments, with the exception of low dose brachytherapy, patients experience high levels of impotence which is still evident after five years."

Androgen deprivation therapy fared the worst, with 94% of patients impotent after two years and 97% after five years. High and persistent levels were also evident with radical prostatectomy (79/77%) and external beam therapy (68/70%), with worse outcomes when the treatments were combined (77/82%).

Dr Smith said nerve sparing surgery improved outcomes slightly, but only low dose rate brachytherapy had relatively low levels of impotence, with 38% impotent after two years and 43% after five years. "Clinicians tend to underestimate side-effects following prostate cancer treatment and invariably are surprised when they learn of the extent and duration of impotence following treatment."

Clinical Oncological Society of Australia President, Professor Bruce Mann, said the study was important in clarifying the level of risk associated with prostate cancer treatment. "Clinicians can use the findings of this study to more accurately inform their patients of the benefits, as well as the potential consequences of testing and treatment for prostate cancer.

"While there are new technologies for prostate cancer treatment in recent years, we need a follow-up study like this to confirm whether these developments have been able to reduce side-effects like impotence."

Source: Clinical Oncological Society of Australia